Before I buy. Second opinion.

[FishFind]

Ok been attempting to fix this problem for a while now.
It is a 1998 blazer 4wd, 4.3l
It has code P0740 comes up just seconds after being reset.
I have checked the Positive power feed wire to the tranny. I have replaced the internal wire harness and tcc Lock-up solenoid. "tested before I put it in too"
I have replaced the Valve body and separator plate. "I had one off a s-10 I knew was good. I still get the P0740.

I have checked and switched the wire on the blue wire harness pin10 wire that is what grounds the tcc. All good. Still does not work

I then connected a wire to the neg side of the batt and connected it to the wire harness pin 10 wire and connected a toggle switch between. When on the highway now I can flip the switch and make the tcc lock and watch my rpm drop by about 400.

From what I can tell my VCM is bad and not telling it when to ground and lock-up.

Should I get a new VCM?

[gmtech1]

I don't have a schematic in front of me, but it sounds like you covered it all. I'd say you are on the right track.

[FishFind]

Also I see some on ebay that they will program it before they ship.

I guess you can just put it in and it works. Ever heard if that is true or not?

[gmtech1]

I would be a little leary of that. Do some checking on the company before you buy, look for reviews.