Friends,

I have a '03 Jeep "Rubicon." I had a FTS 4" short arm "Ultimate" lift installed and increased from stock 31" tires to 33" MTR's.  When highway driving, any slight incline seems to "bog" the engine down when in overdrive. I am only hitting 2000 rpms at 65 mph in overdrive.  If I flip the overdrive switch off, power obviously increases and gives me plenty of power but what a pain when driving on the highway having to flip the switch off and on.  Called my local Jeep shop and they suggested going with 4.88's.  Is this overkill?  Will this correct my problem and will I be screaming on rpm's at 70 mph?  Thank you for feedback.

I don't know how you're calculating your speed, but if  I think you're actually doing about 61 not 65, if you're running 4.11s and a .78 od with 33" wheels, which speed is  too low for od. Having said that underbody air influences and rolling resistance have both increased, causing the engine to work harder. To me the 4l starts to kick in at about 2150 rpm, anything under that in 1 to 1 or overdrive doesn't have much push. So want want to stay around there and above to cruise, and you're a couple of hundred below. 4.88s mean a speed of 70 will run you about 2700rpm, and 80 3100. 2200rpm, nice and comfortable for the jeep, is going to see you poking along at 57mph, waving to 1970 VW microbuses as they cruise past. So 4.88s would be too deep. Somewhere around 4.35 would get you back to stock, but the additional rolling reistance means it needs a bit more twist. You're between a rock and a hard place. But between realizing your true speed, and maybe getting a bit more power through a trickier air intake, you'll be OK with what you have.

Groo, can you check the math? Not my long suit.

There is a guy in our club that has a 06 Rubicon Limited with the stock 4.10 gears. He has a 4" lift and runs 35's. he says that he only has to shift out of OD when going up steep hills. If you don't like what you have change to 4.56 gears. they will work the best. If you plan to go to 35's later on, put the 4.88's in now and save some money.   

I run 36x13.50's with 3.55's and I don't have much trouble with any hills. I can hit 50 or so. But I am slowly beginning to think that I have a magical 4.0L because I have more power than most of my friends who run 33's. Weird.....  

There is always the exception to the gearing issue. I know a guy that has built a rock crawling CJ 7, he runs dana 44's front and rear with 3.73 gears and 37" tires. The spicer 18 with 6.32 granny tranny and transfercase sith a Tera Low kit gearing does all of the reduction. What most people dont think about when changing axel gears is that the pinion spline count goes down and you have less teeth on it to engage the ring gear. I have 5.38's in some dana 60 axels and the pinion only have 9 teeth on them.   food for thought.