Hey guys need some ideas. 2006 6.0 HO Crew Cab Sierra. The last 2 days on the highway the truck is running 600-800 rpms higher then it normally does like its not hitting over drive or locking up? No other driving issues (no slipping or hanging shifts) My whole family has drivin GM's so I'm ussed to the random cold morning hard hanging shifts and all there weird random trans problems. Never had one continue to do it. Any help appreciated.

 

Sounds like its not hitting 4th or the converter is not locking. What rpm is it turning and what speed? Also what rear gears are in it?

 

Truck has 3.73's in it. At 80 the rpms are at about 2500-2600. There usually never that high and with alittle go pedal the drone will get loud because it has a load on it. Now its like the motor is off its bottom end and I can watch the fuel gauge move haha

 

If I recall you should be at roughly 2000rpm at 70mph with 3:73 gears roughly depending on tire size. What size tires?

 

How many miles are on it? Could be a bad 3-4 band? I wore mine out at around 100k. I do a lot of highway driving and im usually flowing with traffic that moves quick around where I drive. Mine didn't slip in any gears but when I would get on the highway my rpms once I got upto speed would start climbing. Had to avoid highways towards the end. In town driving it was solid.

 

I had a similar problem after a trans swap. Turns out when I hooked up the PNP switch, one of the pins wasn't seating properly.

 

Mine did something similar. But i logged it and saw the converter slippin even with 100% duty cycle commanded.
New torque converter for $100 and still rockin.
This happened with the 60e and 80e. About 5 years apart.