gas mileage/rear end

[robandmarla]

I have a 2000 old body style, chevy 2500 4x4 crew cab. The engine is a 350. I am only getting 12 miles per gallon tops. The rear end per the code in the glove box is a 3.73. Does this horrible gas mileage sound correct? I thought this was typical for a 454 not a 350. Could the rear end have been replaced with 4.10 gears, if so how could I tell?

[GM-Tech]

There are a lot of factors that determine gas mileage, with driving habits/conditions being the #1 factor. For a big truck such as yours and with 4x4, 12 mpg doesn't sound all that unusual.

 

The only way to tell if someone swapped in a 4.10 is to count the teeth on the ring and pinion and figure out the ratio from that.

[Trouttrooper]

I'd say that's about average gas mileage.

 

You won't see much of a difference in mileage between 3.73 and 4.10. I've had two identical work trucks with each gear ratio and the mileage was pretty close. 3.73 gets better empty but the 4.10 got better with a load (gee go figure )

 

Another way to tell gear ratio is jack up the rear axle (both tires) put the truck in neutral and count the number of axle rotations vs. 1 tire rotation (turn by hand). Hard to explain but if only one tire is off the ground the differential will mess up the formula. Anyway you should be able to tell the difference between 3.73 and 4.10. 4.10 will get 4 definite rotations plus a tad more, 3.73 won't quite make 4 rotations (If I can handle this complex math then anyone can )

[swilliams1005]

I have the same truck for the most part but i have the 454 with 4:10 rear end and im getting 14 around town and 17 on highway but i have a tuned computer but if you look at my truck i get on it pretty often.