I've got an 04 Silvie 2500HD CCLB 4X4 with a Century Fiberglass cap,342 gears, and I keep my E-rated radials pumped to 80+PSI, gas shox

6.0L -LQ4-with 4L80E trans. Religious maintenance, 18MPG Highway,BUT, I drive like a nun.

Noticed a 3MPG bump when I installed the cap, DOUBLED my mileage around town, as well as a 3MPG highway bump up when I went to the 342s.

I'm currently seeking to get OBD II-laptop info as well as fuel/air ratio gauges to log and possibly re-map my injection...

 

Your not the only one that feels that way. been there done that too.

I get an average of 12.5 MPG on my Silverado but like others say , "Its all in your foot"

 

My foot is very heavy, I never putt around and I drive either my 2000 Z71 or my 2009 Silverado daily. The 09 definitely gets better gas mileage because everything is stock and it has 2K miles on it. You pay to play! Its worth it!

 

I have had to fill my truck up 3 times now, and all three times, I have gotten 17.7XXXX MPG's. That's VERY good, IMO. I am not exactly a grandma, but I don't beat on the trucks I drive either. My old Dodge that I had (95 with 160K on the clock, flowmaster ehxuast, best spark plugs/wires, list goes on) got me a best of 18, and that was driving like a grandma, on the highway only, 55 MPH. With all the crap I did to it, I was hoping to get better.

I imagine once I get an exhaust for my truck, and an intake, I will get worse. Not because they don't increase mileage, but because I love the sound of a good exhaust, so I will want to be hearing it constantly.