Ok I'm aware of every vehicle being different I'd just like to know if I'm over looking something... So I took the truck on its first road trip since the motor swap wasn't to impressed but can't complain to much, filled up the tank with 23g drove 336 miles 95% hwy miles 70-75mph. so I filled her back up today and she took 21g so that put me at 16mpg which seems kinda low to me. I had an 05 Avy pretty much same exact mod besides 4.8 pistons and she gained 2-4mpg after the mods and I would imagine a hell of a lot heavier than the Sierra. Only thing I can think of is my injectors(stock4.8)are maxed out at the moment I plan on installing nnbs intake after I gather the parts. Will maxed out injectors hurt mpg? Rebuilt motor has 1100 miles on it so its not like its an old engine

 

Wow no reply

 

Tire size?

 

Running the same gearing and tires? The compression bump of the flat top pistons increases efficiency so a bit was gained there. With 4.10s I don't think you are doing too bad going 70-75. It is always best to average it out over a couple of tanks anyway. Are you tuned?

 

305/40/22

 

Actually I was running same gears but with 305/35/24 and its tuned by black bear

 

16 mpg at 70-75 mph, with your setup and those heavy-*** 22's sounds about right.

Slow down to 65 mph and gain 2-3 mpg.