I dont think a change from 3.08 to 3.55 wont drop the mileage to drastically or even to 3.70 but i if you got 4.10 or something like that your highway mileage will go down i think anyways....

 

Avator: Yeh, have your preferred weight range before looking around. From past experience towing a car hauler etc, and with the current truck, I figured anything under 5K pounds would work (dry weight) relative to my truck. The lower the better of course. Compromise for size and weight was this Cruiser RV "Fun Finder" 210. Not what I planned on getting, but that was what was available and seems to work for what I needed an RV for.

My objective is to keep this truck one more year and be able to carry a load of the trailer and a motorcycle in the bed under 500 pounds. My tires are due soon, so tires with a slightly higher load range is my next factor. Changing the rear end is also the next objective. I will probably stop short on having exhaust headers though...input on this site seems varied on that topic. Otherwise, air filter and rear-end change along with the recent tune-up and oil cooler and transmission coolers, this package should work for me, keeping max load around 7300 lbs.

Anyway, lot of input here, so I'll stop...good luck...

Scotchale:
98 F-150, 4.6, Ex-Cab, Long-Bed; 3.08; 274K miles!

 

Hey - don't stop with your advice.... all is welcome.

 

No apology needed, especially since neither of our links will work . Just trying to help each other out.

If you didn't find it, type 'Ford Owners manual' into Google and it should be the first thing to show up.

I wouldn't expect too much of a hit on mpg from the gears. It might even get better (especially with a load). My '99 gets over 20 mpg regularly with strictly HWY driving (70+ mph, usually well over that) even with the 3.55's. That's with a fully loaded tool box and stock size tires. Mine's a short bed and they tend to get a little better mileage from what I've noticed on here.

Are you planning to do a gear swap now? If so, I'm not sure exactly what to recommend. If you are going through the expense though, I wouldn't go lower than 3.55 (numerically). A 4.10 would be a big change power wise, not sure on the MPG hit. It will probably depend on the load and speed. It's possible for it to go up even with those (I wouldn't promise it though). I would ask around here if anyone's done it.

Your GVWR rating is the same as mine. A gear swap should set you up for towing.

 

If you plan to tow...I would go with either 3.73's or 4.10's. I plan to install 4.56's in my truck (4.6, auto, 3.55LS) this spring/summer. However, I am running 33" tires, and plan to go to 35's in the future.

With my stock 3.55 gears and these 33" tires...my RPM's at 65mph are only 1800. The slightest hill, or even a headwind, will cause it to downshift. Plus...these 4.6's have no ***. Especially with over sized tires.