My 98 auto ran with 33's and 3.73's for a long time and it was actually pretty good on the street, off-road - well not so much. When I upgraded my axle from a 35 to a 44 I debated for a long time what gears to use. I ended up choosing 4.10's and for me they are the perfect compromise. I can run all day on the freeway and the RPM's are OK. Off road the auto hides a lot of the problems of being geared too high.
I also considered keeping the 3.73's and dropping the gearing in the transfer case for off-road. I can't remember why I didn't do that, but it still seems like an idea.
When I had 33's on my jeep with 4.10 gears, the rpms were a little over 3000 rpms on the highway at 70mph. That sucked. In florida heat and working the motor that hard, the coolant temp was always a tad over 210 (more so than most jeeps). Also the floor boards got rediculously hot.
I'm riding on 35 inch tires now with 4.10 gears and couldnt' be happier. If your jeep is a daily driver w/ 33 inch tires and you see the highway a lot, do not get gearing >4.10 IMO.
what is the optimal cruising rpm for the 4.0 with a 32rh. I have the 3.07's with 31's and i hate it I'm debating on throwing down the cash on one of those bolt in 8.8's but I cant decide on 3.73's or 4.10's my jeep never see's speeds over 60mph and is a spare vehicle. I will eventually upgrade to 33's
I have the d44 and 3.73's (all from factory might i add) and 31's, its just about perfect for me, other than the long highway drives. I will do about 70mph at 3,000rpm which is a bit more than I and the Jeep like, especially since we are doing it in Georgia's low country where our heat index is 110.
I will be moving up to 32's pretty soon and hopefully it will be exactly where I want it. It will be the perfect set up for a DD/trail rider. IMO
I have 32s on my Sahara 5 speed which had a factory D44 with 3.73s that is currently being repaired. This is my DD and that combo was perfect. Was getting 16.5 mpg on my 76 mile commute. I'm running on a temporary D35 with 3.07s right now and it is downright horrible. From the top of 4th gear on, I can't get out of my own way, now get 12 mpg, and and loose speed on the slightest incline. One thing to consider with regearing is that your auto currently has 3.07s in it. To go to any of these gears, you'll not only need the $180 ring and pinion set and the $120 master install kit, but you'll also need a new carrier which is another $100. That's $400 in parts and anywhere from $250-$500 to set it up if you can't do it yourself. This is per axle! A D35 just isn't worth that much investment. If you found a resonably priced D35/D30 combo with 3.73 or 4.10, then fine, but I wouldn't try to convert one to that.