The truck is horrible on the highway through hills and such. I'll be slugging along around 70 MPH @ 2100 RPM, start to hit a slight inclimb and the truck will slow down rapidly until I have to drop hammer to keep up with traffic. It shoots out of OD then sits and cooks at about 2500 RPM til I top the hill then itll regain speed and go back into OD. I know its a lack of HP and torque, but can gearing my truck fix this?


its a 98 expy 4x4 with 285/75' BFG's. . .

I'm getting around 300 miles to a tank per week it seems. Thats with little warm-up time, 75% highway driving, and the rest city. Most of the fuel is wasted cause the truck just constantly has to drop out of OD to make these hills. . . what to do. . .

 

Well the tires aren't helping any. I noticed a drop in performance when I went from the stock 255/70r16s to my 265/75r16s. Just because the bigger tire is heavier. If you go to 4.10 gears or something similar, you're going to notice a nice difference in city driving and your around town MPG but will definitely lose MPG on the highway because you'll be cruising at a higher rpm. If it just started you can try other things. For one, change your fluids. I assume you regularly change your motor oil. Don't forget about your transmission and your differentials. For the price of buying gears and having them installed, you can purchase an entire new exhaust from the headers back and an intake to let the truck breat a bit better. Also, you can try electric fans and maybe underdrive pulleys. They'll free up some horsepower and improve your mileage at the same time. I actually have everything I just mentioned sitting in the basement now ready to go on.

 

Oil is every 3k, synthetic. I have done both diffs about 10-15k ago. Just put in a new trans filter and had it flushed about 10k before I changed the filter. T-case ofcourse has been done. I had cut the stock muffler off, but still have the stock cats and what not.

I'm pretty sure tbhe next thing I'm doing is plugs and wires. I'd imagine they have never been changed

 

If it makes you feel any better, I have an 02 Expedition and I average about 300 miles per tank. I have 265/75r16s which are slightly bigger than stock. It does dog a bit on steeper inclines. It started when I got the tires. What it boils down to is definitely lack of power, especially for the heavier tires. A tune up wouldn't hurt though. Just be careful with those plugs. Make sure you torque them down as close to perfect as you can.