Just completed a tranny swap last night in a 98 2500 4x4 with 360. After everything was said and done I cranked the the engine and after a few seconds it began to lug down really bad. Even backfiring a little. Check engine light came on but no code reader on hand. I checked a few things with fire and such but nothing was out of place. I decided to go ahead and try shifting the new tranny through the gears. In reverse with foot on brake the engine seemed to bog down even more but once in neutral it ran smooth. In drive it ran smooth. Back to park and it was very rough again. Shifted back to neutral to check tranny fluid. After doing this I shifted again to park and it ran fine. Killed the engine and unhooked battery to clear check engine light. It cranked and ran fine after that. Until this morning when I got in it to drive to work. Same thing. Running very rough in P and R but did fine once in D. Now that it's warmed up it'll idle fine in P. Should note that while I was u Dee the truck I dropped the oil pan and pulled the oil pump to clean it all up a bit due to low oil pressure. Oil pressure is perfect now. Any clue????

 

Did you remove the crank position sensor when you were removing/installing the trans? They tend to take a beating if you don't, and can give you some truly strange running problems. Wouldn't hurt to pull it, and have a look. See if it got damaged, or if any wires got pinched between engine and trans.

Welcome to DF!

 

Thank you! I'll check that. I kinda think the bolts from flex plate to TC may have been over stretched and caused damage resulting in the thing trying to lock up. Idk though. But thank you for the help and for the "welcome".