I've taken this thing apart several times, tried various fixes, chemicals, cleans, and replacements and still have dirty dishes with food or soap particles, scum, etc.

I finally decided what I need is either a new dishwasher or higher water pressure coming from the impeller (not the inlet pump). My belief is that a matching impeller with a larger diameter will give higher pressure so long as it fits in the same space and on the shaft. If a part is close, I can machine it to tolerance.

First, is my thinking justified and workable?

Second, I've come up with these potential substitute parts:
Whirlpool MFG 902461 or stock #AP4110858 (http://www.appliancepartspros.com/whirlpool-impeller-assembly-902461-ap4110858.html)
Whirlpool MFG 4162467 or stock #AP3102109 (http://www.appliancepartspros.com/whirlpool-wash-impellor-4162467-ap3102109.html)
Sears water pump MFG J105-40P (http://www.sz-promo.com/spproduct/127845/2b79212c/impeller-198003a.html)
SZ-Promo.com part #ISP-198003 (http://www.sz-promo.com/spproduct/127845/2b79212c/impeller-198003a.html)
Whirlpool MFG 99002659 or stock #PS2100007 (http://www.********************.com/PS354807-Whirlpool-4162467-DISCONTINUED.htm?SourceCode=3&SearchTerm=4162467)
Part #4162467 (http://www.a-1catalog.com/41upim1.html)

Unfortunately, only a couple of these show measurement grids and none give specific measurements. Before I order ALL and measure against my current impeller before I use or ship it back for a refund, I'd appreciate some experienced help on this. Hopefully, it'll be more than just put in a stock impeller and accept the situation.

I've taken the interior parts out several times, cleaned the filters, jets, and parts, replaced the impeller once, removed all deposits, run commercial cleaning fluids through a couple of times and even changed soaps. I've taken the dishwasher out and inspected all external parts visually after being told about increasing water pressure in. However, I didn't do anything because the rationale for increasing water pressure in doesn't jive with internal pressure once the water is in the dishwasher.

Thank you. I've ordered the part and will try it when it gets in. I'll report back the results.

Have you checked your fill level?

Most units fill to just under the heating element.
Often if it is a low fill issue, you can hear it, the pump will growl because it is sucking in air.
You can check this by adding a quart or two of hot water after each fill during a cycle. If it now washes OK then I would check the screen filter on the input side of the water valve for a partial plug. If dirty clean it. Do not permanently remove it from the valve as it is there to keep crud out of the valve which could hold it open and cause a flood.
Just be careful to not over fill it.

Since I couldn't find an expert here that could give me help on increasing my internal circulating water pressure, and wasn't able to find any specs on the parts list for possible replacement, I had to do the DIY method. I made my own with great success!!

All it took was $1.79 for the top of a regular 5 oz. tuna can and three small brass screws no more than 3/8" long. Since I didn't have plans I had to experiment. So, if anyone is reading this thread here's what I learned.
1. The top of the impeller to housing clearance is too close to put anything on top of the impeller.
2. The bottom has enough room to work - but keep it thin.
3. There is some pressure sensor in the system that shuts down if there is too much water pressure. I had a working model, but it kept shutting off after about 10 second of high pressure, then would cycle again. This cleared up when I cut down the size of the "improvement".
4. I won't cover all the little details except think about rust. Use a can and screws that won't rust quickly. It's easy to replace, but why if you don't have to?

Here's how:
1. Cut the bottom out of a 5 oz. tuna, chicken, etc. can. It's about 3 5/8 dia. and about perfect in final size.
2. Drill a tap hole in the very center. Then carefully cut a 1" hole using the tap hole as a guide. I used a 1" wood bit since it's very thin soft metal.
3. With tin snips or kitchen scissors, expand the hole until it fits snuggle around the ring on the bottom of the impeller.
4. Mark the diameter of the impeller on the metal disk. While doing this mark a continuation line of the impeller vanes onto the disk and another line extending from the impeller vane end through the impeller center to the outer edge of the disk. The idea is that you want to extend the vanes for more thrust of the water as the impeller turns.
5. Cut a line from the outer edge of the disk to the edge of the impeller line along the straight line from edge to center. This will be about 1/2" long.
6. Bend to 90 degrees the tabs along the vane lines so when it's fit in place it literally extends the vanes another 1" (approx.).
7. Fit the disk onto the impeller from the bottom with the vanes pointing up and rotate the disk so they line up with the impeller vanes.
8. Cut the bent up vane so that anything extending above the top edge is removed by at least 1/8". This will prevent contact with the upper housing.
9. Once cut to size and lined up properly drill three small holes in the disk and into the bottom of the impeller to fit your three brass screws. Screw it in place and replace everything.

To TEST - Before you replace everything. Screw the impeller in place and install the cover with 3 screws. Run it on rince cycle to make sure it doesn't stop and cycle. If it does simply use the tin snips to cut a little more off the outer edge of the disk and bent up vanes. Try again until it works right.

You'll end up with a lot more internal water stream pressure. I hope someone can use this.

It's the right time of year so - Merry Christmas!
drkenrich