I think my 99 f150 4x4 has 3:55 rear end gear ratio, but it seems very dead in the top end,is there something wrong with my truck or would a different gear setup make a difference?

 

I have the same truck, and I agree, especially if you have the off road package or larger tires. HIghway driving with a load, there are times when I want just a bit more.

You could get 3.73 or the 4.10 gears.....or for less $ get a new Y-pipe and headers to help with the high end output.

A gibson exhaust would help at the high end too.

 

For all highway driving you would want higher gears. Lower gears help help off the line, but higher gears will make the truck faster at highway speeds & you'd get better gas mileage. Fords high gear ratios are 3.08 & 3.31. I think that the 3.08s are too slow of the line, but the 3.31s are a good combination.

 

I've got the 3.55 gears in my truck. And I too think they are a little sluggish at the top end. But they seem to give me more power than the 3.08's I had in my 83' F-150 off the line. In my opinion, 3.55's are just a good all around gear for getting the best gas milage out of your truck. If your just driving around town, or cruising at 70 mph on the interstate. And they help out if you tow anything too.

 

My 98 with 4.6 auto has the off-road package (17" rims), even with the larger 275 AT/S rubber on them, with the airbox mod it holds high gear better.

I think the 3.55 LS is the best compromise if you won't be doing any heavy towing. For heavy towing I'd go to 3.73.

If your highway driving includes a lot of mountain terrain then I'd also go to 3.73 but otherwise 3.55 will afford you the best fuel economy.

 

The opinion on the best gears depends on the goal:

Off the line - go to lower gears (3.73, 4.10, etc...)
Fuel Mileage -go for higher gears (3.08, 3.31, etc..)
Compromise - 3.55's give a nice blend of both.

I run the 3:08's. I'm not a stoplight racer and I do a lot of freeway driving. I get 17mpg (long term average over 5 1/2 years) and regularly get 20+ on the freeway doing over 70 mph.

At higher speeds the gears start to wash out a bit as wind resistance becomes such a factor.

 

I've had both the 3.73s and 3.55s and the 3.73s are the way to go. The truck is stronger at all speeds and RPMs, and the gas mileage difference is negligable. The truck with the 3.73 had a wicked 60-90 mph punch that was great for interstate passing, with or without a load. Loved it! Still trying to get used to the 3.55s...

 

Higher ratios (lower numbers) don't necessarily correlate with better gas mileage. My 2000 5.4L Expy 4x4 has factory 3.31's. Then I put on 33" tires so my effective rear ratio is now 3.01. I get absolutely no better mileage with the higher ratio. Hence, I'm going to install either 4.10's or 3.73's really soon. With no mileage increase and more sluggishness off the line, I see no reason not to install lower gears. And no, my truck is not constantly downshifting while driving along the interstate despite the high ratio.

 

The larger rolling resistance of the 33" tires offsets the change in"effective" gear ratio. All other factors held equal, including tire size, the 3:08's will generally give better fuel mileage than 3.55's etc...

 

gopher: I was just going to say the same thing you mentioned. 33" tires plow harder through the air.

 

I have a 2002 f150 reg cab with the 4.6l and 3.55ls. I guess it is the size of the tires(275/60/17's) that are boggin this thing down. I had a hard time out running a 4Runner the other day!!!