First post here, fairly sure I posted it in the right place.
I have a 1992 pickup with the 3.0 and automatic transmission.
recently bought this truck from a neighbor, I knew it had some issues and he couldn’t figure it out
after I got it my research lead me to replacing the ecm, which I have done. I got the unit from a company called flagship one, no idea on their reputation, mixed reviews
Now to the current issue, after replacing the ecm it started and ran great. Took it for a test drive, about 15 miles, never once had any issues
got home parked it, left it 6-8 hours, hop in it and put it in gear, rolled about 15 feet and it stopped moving. Put it back in park, shut it off then restarted and the same thing.
finally decided maybe it was the new ecm, unplugged it and plugged it back in then started it and it went into gear. Got it parked and shut it off, restarted it and again nothing. I can feel it going into gear, reverse, drive, 2,1, but I can floor the gas and no movement.
I had a gmc with a problem transmission, I know what a good tranny feels like vs a not good one.
this one felt fine while test driving, but now it’s like it doesn’t exist.
some of my research says shift solenoid(s), or other sensors? Any ideas or suggestions?
the po did swap the transmission, it was the same one, he pulled it from a junkyard.
thanks in advance

 

Do you want to try unplugging the TCM? It lets you shift manually into the lowest three gears after park and neutral.

 

I’ll try that

 

where is the tcm on these trucks? I cannot find it

 

my first gen has it mounted directly in front of the shifter to the top of the transmission tunnel. Under the plastic shroud. Very possible they moved it after gen1 but check there first.