Sudden odd issues after rebuild last Dec

[GP1138]

I have a 2005 Grand Prix GXP. My wife drove the car to work and home yesterday with no issues. She said it was driving normally, and I think she would have noticed these sudden issues.

I got in the car to go somewhere and as soon as I took off, the car kicks into 2nd and 3rd like a mule, and then proceeds to buck between 1100 and 1500 RPM. Kicks back into 1st and then taking off starts it all over again. Doesn't seem to be slipping.

I tried to pull codes but my Wifi ELM scanner doesn't seem to be able to pull them. MIL is already on for a P0420. EBCM is bad, I have actually removed it at the moment to repair and same issues when it was installed and removed.

The trans was rebuilt late last year - the TCC seal took a crap, and the car had the TCC replaced along with the clutchpacks and sensors/solenoids.

Any thoughts on what this might be? I'm going to take it to get scanned tomorrow at Advance and see if I can get some specific codes.

[SgtMarshal]

does your exhaust smell like rottten eggs?

[GP1138]

No, and there seems to be no power loss either.

[Scottydoggs]

drive the car till it acts up, then go to get it scanned. do not turn the car off, scan it running. if you turn it off it clears a pending code.

[GP1138]

It acts up immediately after starting the car - I did try to scan it after a drive but it was with my Wifi scanner which could pull codes on my '04 but on this '05 it's not able to. I'm going to drive it and take it to Advance and see if I can use their scanner.

[GP1138]

OK, went and scanned it and as suspected, throwing a P0742, TCC stuck on. Going to check wiring and such. I cleared the codes and it actually stopped kicking like a mule when shifting, but TAPShift still gives a kick when manually shifting.

[SgtMarshal]

Harsh shifts, P0742

[GP1138]

Late GM vehicles with codes P0742 or P1887 - YouTube

Going to go ahead and do this - looks like this is a great way to find out where the issue lies. Hope this helps someone else that has this issue and stumbles on this thread.