HELP

I would start with the rears before the motor.....3:55 or 3:42 and I bet you will see an improvement, might suffer some in the hills up north though. That Detroit is notorious for good fuel mileage. Although I like Cat, I don't think you will see much improvement in fuel mileage by switching motors. Just my opinion. Oh, you might want to convert that 9sp to a 13.

 

Solid advice.

 

What tire size are you running? There's another issue......24.5 LP's would be my choice, of course on Michelin rubber... I'm sure others will differ on this though.

 

Gotta second (or third) the 13spd. Going with that should help you out right away with both pulling hills and a bump up in mpg.

 

I think you should have known your mileage would take a serious hit "stretching the hell out of it" Going with a 13 over a 9 and changing the gears will gain you something, maybe only a lighter wallet, but I guess it's something. You want your mileage back? "shorten the hell back out of it" or continue to look real cool drinking all that fuel!!

 

11R22.5's or lopro 24.5's same overall diameter would be the right tires for those 3:70 rears. I would not have lopro 22.5 on a truck set up like yours. It would put you about 68mph @ 1500 rpms. 11R24.5 would drop rpms even more.