right now i have a c4 tranny and 31 inch tires with a 4.11 posi..... my problem is, im moving 700 miles away and gas mileage is horrable on the highway! .... I have access to some 2.41 posi gears... would that be too much? or what should i do to get the max MPG?

 

Too little info. Is this your '62 F100? If so, it's a 9 inch diff with a drop out carrier, right? You can just swap those tall gears in there for the trip and keep the other carrier, right? 2.41's are pretty tall, but you're on the highway....

Lots of work for a 2 day drive....

Or are you going to commute regularly? (buying more oil co stock in anticipation of a "yes" answer....)

 

2.41's are REALLY TALL for 31" tires. Will you be driving thru the mountains on your trip? Will you be towing anything or carrying a heavy load in the bed? What size motor is in your truck? Going to too tall a ratio with not enough power or too much weight and tall tires can actually lower gas mileage if the motor has to spend too much time at wide open throttle to get going and pull the hills. I would just leave the 4.11's in it and drive slower on the trip. You'd be surprised how much gas you can save going 55 instead of 65 on a long trip.

 

1) make sure everything is tuned properly.
2) drive like there's an egg under BOTH of your feet.
3) gear so that higway cruising rpm is just under your dyno tested peak torque rpm. Ignore parts people claims.
4) slowing down really does make a difference. Aero-drag sucks!
5) manuals get better gas mileage.