Ok, you have established that your dedicated drain pump IS pumping. You have also established that your drain system's flow rate is slower than its design predicts. So what's slowing this drain system's flow rate? While that system is fairly simple, access to see what's going on is terrible, so its best to start with the most likely causes and work toward the least likely causes.

A likely cause is an obstruction in the drain flow passage way. Start at the most-easily accessed point which is at the connection into the garbage disposal. Determine if that is partly obstructed.

This system includes a one-way limiting flow "check valve" which should prevent any garbage disposal overflows from feeding water into your dishwasher. So you should not be able to blow water or air backwards through that check valve into your dishwasher.

More obstructions. Check to see if the rubber drain hose has become kinked, obstructing flow. I know this doesn't seem likely since it was probably not kinked before when it was flowing well and the dishwasher has not been moved since then. But that hose may have been resisting bending pressure for many months, which resistance declined with each heating and cooling cycle, allowing a kink to slowly develop. This is a new one to me. If I had not seen it, I'd have been skeptical that this would occur.

Inside the water circulation system is a screen and particulate chopper. If someone in your home LOVES recycling glass containers and ends up washing off paper label parts, that wet paper mass can form a very effective filter-plugging slurry of loose water-entrained fibers. Access that filter as has been explained in many discussion threads. Use a safe light source to enable viewing as much of BOTH SIDES of that filter screen as possible. I found one where the grinder-chopper had cleaned most of those fibers from the intake filter flow side yet the other side, and probably the filter holes, were obstructed with what I think were paper fibers. Don't run paper through your dishwasher. Paper was a wet slurry and can be returned into a wet slurry again within your dishwasher, plugging your filter.

If your drain system is not obstructed, is your pump spinning up to full speed? Is the pump impeller blade set clean and still shaped about as it was when it was new? Broken and worn out impellers can occur if they pump debris larger than should ever pass through the filter.

The pump motor has one armature support bearing on the "wet end" of the motor. It is SUPPOSED to never get wet because there is a water-isolation seal between the fluid and the motor. But in fact, those seals begin to leak enough water so those went-end motor shaft bearings get wet. They could have specified a stainless steel shaft with a stainless steel bearing so they would not rust. But they didn't. The makers should be embarrassed. But they aren't. They might be angry that anyone points out how easily they could have prevented this common failure cause in their dishwashers - rusted motor wet-end bearings. If your original rustable wet-end bearing is slowly rusting toward becoming trash, your motor's performance will slowly degrade. It starts with increasing noise and eventually moves to conspicuously-slower motor rotation speeds and ends with motor lockup, incorrectly described as "worn out." That failure mode is obviously NOT wear for crying in the beer. If the drain motor is spinning slowly, it can't drive the water impeller fast enough to impel the water up the drain line with much force.

If this system were mainly formed from see-through plastics, you might be able to better see what's going on. But even then, your view through that plastic would be impaired by scum that would attach to the inside surfaces. So you might clean that with mild acid, like vinegar.

I've read others suggestions about leaving an acidic solution like vinegar in dishwasher sumps to remove lime and similarly removable trash that acid might attack. One thread even described using Draino or competing products. I have mixed feelings about that. Granted, I see the merits of acid cleaning. Acid cleaning with a circulation pump run as a recirculating loop over a weekend works wonders on limed-up water heaters. But in the circumstance of usual dishwasher sumps, sealed by notoriously-leak-prone pump-shaft seals? Too tough for me. What I envision is dripping mild acid or strong caustic Draino onto already-compromised rust-prone motor shaft support bearings on the motor shaft's wet side. Call me conservative, but I don't like adding even weak acid to that environment. I fear it could and would accelerate pump wet-side bearing failures. Some popular dishwasher cleaning products are quite acidic. Naturally, their makers would claim that pump seals should protect those pump motor bearings from acid exposure. According to that absurd theory, they would not be directly destroying both dishwasher motor types - circulation and drain pump. Are they kidding? Get serious. They have to know that assumption does not describe typical dishwashers in American homes. I'd think that they would live in fear of a class action suit from directly turning millions of dishwasher circulation and drain pump motors into trash. But maybe that's just me, concerned about down-stream effects these product makers would like for everyone to pretend don't exist. Especially those who own and use dishwashers.
John

I have a KUDK031TBT3 which has this same problem. The repair company, A&E, has been out about 12 times to analyze or replace parts for a Kitchen Aid Warranty that expires in early March of 2013. They have replaced the control panel, pump, hose, rinse aid dispenser. What's left but your motor idea? My wife also heard the supervisor tell the tech. that there have been instances where they have not been able to fix this problem.

Any ideas on what should we do?

By computer do you mean the control panel? That was the 3rd thing they replaced. The only things left to replace are the pump motor assembly & the inlet stuff. The saddest thing is that A&E will not declair it unrepairable & neither will Kitchen Aid who I bought the warranty from. If they would we could get a new orr rebuilt for 25% cost. But to be honest I am afraid to go that way.
Thanks for getting back to me so soon. And I hope you don't run into anymore Kitchen Aid dishwashers with this virus.
Thanks again

The root cause of the machine leaving an inch of water after running is a faulty flapper valve in the hose. The valve is located inside the rubber elbow at the pump outlet. To fix it, remove the hose completely and flush it out. Bend the elbow straight then poke a screwdriver down in the hose. Once the flapper is free you should be able to blow through it as easily as through a toilet paper role. If there is any resistance, the flapper is still stuck. When the flapper is stuck, it still allows some flow, and this is why the pump is able to pump somewhat even with it plugged. Once you get the hose free from resistance, reassemble. Be aware that the hose is tricky to remove, because it loops up the side of the machine, but it is worth removing it completely to do the required work. I suspect that some techs are only replacing the hose from the back of the machine to the drain, and as a result fail to fix the problem .

For your KitchenAid dishwasher not draining, there could be several reasons for it. It may be due to a faulty pump or a clogged drain hose. To quickly solve this issue, it is recommended that you inspect all the electrical and mechanical components related to the drainage system of the dishwasher. Once you identify the problem, you can implement the necessary fixes to resolve the issue.