At 60mph...
 

I'm at about 2200 rpms or so. What is up with that? I can barely make it to 70 with the engine being defueled. Is my truck jacked up? I have 285/75/16s and the speedo has been corrected for them. Please help.

You have a 4.10 ratio rear end.

Would 3.55s really help me much? Is it worth putting out the money to have them changed? I'm getting around 16mpg highway right now. I think I need to have my timing done, and fuel plate.

Ummm... If your getting 16mpg right now, you will prolly only see a few miles per gallon more with 3.55's... I wouldnt change rear ends unless your always on the highway. You will love the 4.10 if you ever want to pull anything.

Don

a 3k gsk or a 4k gsk and a 100 plate will take care of the defueling.

Sounds good. I will probably see slightly better fuel mileage when I get the timing, fuel plate, and AFC done.

The timing alone will make a big difference.

Do you have 4.10s? I am glad timing will help.

3.55

I only had my truck about 200 miles before I put the plate & GSK in, but the timing was a few tanks later. I picked up about 2 MPG with the timing bump. I average about 18.5 empty, can top 20 if I do all highway and keep my speed about 68.

Ouch, so I'll top about 18mpg. Oh well, I still love the truck.

FWIW- I have a fairly heavy foot, drive in town a lot, and idle a lot...

Nice thing about these trucks is mods are free or cheap, that leaves money for bigger mods. I'm gonna shoot for 20mpg.

I got 4.10's in my current truck had 3.55's in my old one. I really like the 4.10's when I gotta pass somethin but I miss 21mpg's. I was wondering what a truck is like that has 3.55's and has been bombed? My old one ws stock. Could't pass a vehicle unless the other lane was clear for about a mile.

Nice thing about these trucks though, if you can't get 24 mpg you can make biodiesel and not worry about it. That is what I am going to do.

Something doesn't sound right here. 2200 rpm at 60 mph sounds too high for that tire size, even for 4.10 gears. 2200 rpms with the transmission in 5th gear (.73), 285/75R16s (32.8"), and a 3.54 axle gear ratio should put you at about 80 mph. 4.10 axle gears would lower that speed to about 70 mph.

Have you actually clocked your truck over a known distance to check the accuracy of the speedometer? Seen if it takes 60 seconds to travel exactly 1 mile at an indicated 60 mph? If that checks out, I think that your tachometer may be reading too high.