Transmission sensor problems P1810

I started this thread about 2 months ago and thought I'd finish it for anyone searching archives looking for solutions to their own P1810 problems. Plus I had a bit of a quandary with the VCM that never got
resolved this time around, which I hope could be addressed if anyone has an opinion.
P1810 concerns the Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) located in the transmission. The TFP consists of five pressure switches (three NO, two NC). The code P1810 sets when the VCM detects an invalid state of the TFP Val. Position Sw. or the TFP Val. Position Sw. circuit by deciphering the TFP Val. Position Sw. A service bulletin has been issued that the TFP switches can get contaminated with metal or other junk from the transmission fluid so that the TFP switches fails and P1810 sets. The new TFP has a plastic cover to help prevent contamination of the switches (note: mine had this plastic cover).
First I checked continuity of all wires and TFP contact to ground and VCM.
Then I removed the TFP unit and found a normally closed switch that was intermittent. I cleaned up the switch (they are a simple design) so that I was getting good conduction in the normally closed position and an open circuit when the switch was depressed. All other switches worked OK. I never resolved a problem with the VCM. The Vehicle Control Module (VCM) supplies the battery voltage for each of three range signals to the TFP switch by way of the 20 pin connector on the transmission. By grounding one or more of these circuits through various combinations of the pressure switches, the VCM detects which manual valve position you select. It seems simple enough; however, when checking my VCM voltages to the TFP switch I noted that one of the three wires was not giving 12 volts (rather <4V), so I went to a reputable auto recycler and purchased a replacement VCM, but it had a similar low reading on the same wire, so I replaced that VCM but had the same result. At this point I didn't know what to think. The auto recyclers assured me they were functional VCMs when removed from vehicles. The intermittent TFP switch should not have shorted out the VCM, so I assumed it was some kind of a mistake (perhaps I was overlooking something?).
Hopeful that the switch I repaired on the TFP was the cause of P1810 and not the incorrect VCM voltage I was seeing, I put everything back together (not a very hard job except for the messy transmission fluid) and tried out the vehicle. P1810 set again within a few days. OK, I didn't mind spending $20 to try a couple of used VCMs, but maybe that just created more uncertainty. I decided to forgo $400 on a new computer ($300 + $100 to flash ROM) and $60 on a new TFP switch until I get a little more info, though I assume replacing both will solve the problem (BTW not that I suspect this anymore, but the dealer replaced/rebuit the transmission at one point in the vehicle's life). For now I've obtained an E-check waver for the work I did on the vehicle, but I will have to address the problem again in two years.
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If I recall correctly, there's a tsb on many models for this code which reports an issue with valve body wear.
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