2002 Tahoe transfer case problem; need advice
 

First time user on this site, but have always been a DIY'er.
2002 Tahoe 4WD switch stopped working and all switch lights went out and the "service 4WD" trouble light came on. It felt like it was stuck in Auto, so I took it to the dealer. They ran "trans Case Diag III" and got "no codes stored" BUT told me it was the TCCM and wanted $659. to replace it with NO guarantee that it would fix the problem. (Mechanic said it was not supplying 8 volts to the encoder module) So I ordered one on line for $160.and replaced it myself. I also ordered the dash switch and replaced that. No change.
Next I decided to replace the T/C encoder motor assembly and the front axle actuator. When I did that the T/C is now stuck in neutral.:confused:
What did I do wrong? Any suggestions on what I might have missed?
More info:
1) The 4WD switch lights flash on at start-up but immediately go out.
2) When I installed the new T/C motor assbly I had to turn the gear inside the T/C one click to line up. I did NOT turn the gear inside the new motor.
3) The TCCM did not have the same OEM number on it. I complained to the company that sent it to me. They said it was compatible and did provide a list showing that. OEM#12577410 vs. #15749703 (and I think it was a used part).