I have a 06 silverado with a 6.0 that won't pull , It didn't have this problem when I first bought it but once it started I haven't been able to find a fix. I have been thinking its a motor power problem maybe transmission. when I am not pulling anything to go up hill and try to keep a speed between 50 and 70 is impossible to hold the pedal in one place speed quickly falls off, from there I have to punch it it shifts into passing gear and if I put it in cruise it will hold the speed but it will shift up and down the whole way. To pull a local hill with my sport quad I only get 6 MPG can only do 55mph completely punched and it shifts in and out of passing gear very frequently. I am a mechanic and have done all the basic matinenance and still no fix. Talk about a gutless truck.

I have an 06 Silverado 2500 with the 6.0. I have taken it to dealerships to several local shops and no one can tell me why I have a hard time pulling one sport four wheeler. When I first got it I could pull anything and still get decent mileage. now best 6 MPG with my one wheeler...Before this I got 14 MPG and 11 or so while pulling now 12 at best and 6 MPG while pulling ANYTHING. I have been told my converter is not plugged, I have done a tune up. Its ridiculous I even put a aftermarket intake on it and it actually made it worse. The first five minutes I could tell a great difference but then the computer changed the settings and it mad the power even worse. My next step is to get a programmable chip to see if that fixes it.