Im in the same boat as you... have the 05 1500HD with the 6.0. Lifted with flowmaster exhaust and 33in tires i was getting 9.5 in city with lots of hills and curves.. just got banks cold air intake and banks automind programmer for it and i am now getting 11mpg in city and 13 on highway... so that is how much it helped on my truck if that is what you were wondering... Im still not sure if it was worth spending as much as i did on it but for now it seems like its been worth it... i was considering on trading in for a newer truck that would get better but for now im gonna stick with this one.. maybe later on down the road i will do that but the cai and programmer can maybe get me by for a while... they cost me about 300 for each