I've gone through almost every thread related to my problems to no avail. Looking for input on why all of a sudden my s/e light came on and the tranny began slamming every gear like I got hit in the ***-end. I've reset the monitors by unhooking the battery but it only works when unhooked overnight. When hooked back up she runs great until I hit around 65 mi travelled then s/ e light comes back on, tranny slams gears again and gas consumtion is greater. Also rpms at idle go from the normal 700 to near 1200 and hold. Changed filter, did visual inspect for shavings, nothing on magnets, changed fluid 3 times and it continues. Any input would be much appreciated.

Edit: 4.3 vortec v6 auto tranny

 

Why don't you start by listening to your truck... When the service engine light comes on, it means that a code has been stored that gives you a clue into what the PCM thinks is going wrong. that is the first place to start, even before screwing around inside the transmission.

 

Got a code back 1080 (or something like it don't remember) rear bank running lean. All I got. Nothing pertaining to tranny.

 

Pxxxx is the format. Get the exact code, post it, and we'll go from there. 1080 doesn't come back as a valid code...

 

P1870 is what I just got. 1. Trailer towing may set code. 2. Check fluid level. 3. Internal transmission fault.
Tranny component slipping. Tranny is in 4th gear with TCC engaged and ECM has detected excessive slippage when comparing the input shaft speed to the output shaft speed.

 

That's a bit different now isn't it. This may not be something that can be diagnosed from your backyard. Run through the diagnostic chart below and see what you can do. Beyond that, you can run a search for "P1870" to see what others have run into. You may have to get it to a shop that can run through the diagnosis.

P1870 - Transmission Component Slipping

 

Thx man, will get back on when I figure out whats up. Thx again, u gave me more info than any dealership or repair shop I asked. At least I can now start in a direction.