Originally Posted by bruce51d
if you're just drivin it unloaded maybe you should get a little beater car that gets like 30+ mpg. i've read that you can't go any lower on the gears in the 450's but i'll have to research
He doesn't want to go lower on his gears, he wants better mileage- lower rpm's at speed - so he wants to go "higher", or opt for a set of "highway" gears, which means anything higher than 4.88's.
And I could be wrong about this, but I'm pretty sure my brother's box truck has higher gears than 4.88's. Maybe like around 4.10's, so I think you can run a higher gear set for you truck.
Do you have auto or manual? If you are manual, and you can find 3.73's gears then I wouldn't think twice about it, but if you're automatic then I'd probably go no higher than 4.10 if you're gonna pull 15,000 + lbs.