2001 2500 4x4 5.9L6 Auto trans.
Melded together a 2001 and a 1999. Have 2001 ECM on engine, but am sure the PCM on body is still the 1999.
Will this cause these issues?
1. Will only go into low manually. Will not downshift on it's own.
2. Will not upshift automatically.
3. Will not make overdrive, but is not spongy and does not feel like it's freewheeling. (like every other car I've had with a bad OD clutch set.)

Trans was the original 1999 trans, but I swapped out the electronics inside with new 2001 stuff.
Am I wrong to believe the PCM is or may be causing these issues?

 

Electronics mismatch. Things changed from 99 to 00, and the pressure sensor is giving the PCM readings it simply doesn't understand. Change out the governor pressure sensor/solenoid, and it should resolve the issue. Keep in mind, I think the internal connector on that harness for the TCC and O/D solenoids also changed, so, probably need to swap those out as well. According to theory, you can do it without dropping the valve body, just gotta be lucky.

Ok, read further down your post, and you already have the correct year electronics installed.... Are you getting any codes? Is the trans temp light coming on? Is the O/D off light coming on??

 

No O/D light. No codes. No trans temp light.

 

Diesel? What year PCM is bolted to the firewall on the passenger side? The one with three(?) connectors? If that's still a 99, then the electronics don't match.

 

[QUOTE=HeyYou;3497428]Electronics mismatch. Things changed from 99 to 00, and the pressure sensor is giving the PCM readings it simply doesn't understand. Change out the governor pressure sensor/solenoid, and it should resolve the issue. Keep in mind, I think the internal connector on that harness for the TCC and O/D solenoids also changed, so, probably need to swap those out as well. According to theory, you can do it without dropping the valve body, just gotta be lucky. [If I push the button the O/D light comes on, but changes nothing. No temp light and no codes.

 

That's what I was thinking, just wanted another opinion before I shell out another wad of cash. I believe there are 3 connectors on pcm. Can't read the p/n to verify year. I inherited the truck when my father passed last year. He did the engine and body swap. and he's not around to ask.

 

I know the diesel has two computers... one dedicated engine controller, and then the Main PCM on the passenger side firewall. The one on the passenger side firewall has to match the electronics in the trans. So, 99 PCM, and 01 electronics isn't going to play nice.

 

Sorry for your loss.

Between you, and the good folks here though, we can figger it out.

 

I had that happen to me. Turns out the TCU within the PCM was fried due to the transmission connector wires shorting. It would only shift manually. All problems were resolved when the pigtail was repaired, and the PCM was replaced.