Sub'd
After towing my 18ft R-Pod (~2400lbs) on it's first long haul trip (1100 miles), and getting 10.5mpg, I'm definitely looking for a solution to my 4Runner's lack of power. I love pretty much everything about my 4R, except the power. My daily's (Audi Q5 tdi) 3.0 v6 makes the 1GR-FE look pathetic with it's 428ft-lb. Unfortunately since my Q5 doesnt have a beefy suspension or hitch (and cant go offroad), I'm stuck towing the camper with the 4R. The idea of the 1UR-FE swap also came up during my 22+ hours of towing. More recently, I had the idea of just swapping the 5-AT (A750F) for the 6-AT (A760F) found in the GX460, Tundra, & Sequoia. Since I spent almost the entire 1100 miles in 4th gear, I looked at just re-gearing, but 4.56s on my stock 32s seems too aggressive for all the highway driving I do.
From what little I've been able to find online, the bell housings are supposed to be the same. Gears 1-5 are identical, with the ratio for 6th being .59 (5th is .72). Pair that with a 4.88 re-gear, and 6th at 70mph will be about 200 rpm higher than stock. My hope is that the slightly higher cruising rpm would be enough to keep the 4R from down shifting at the slightest increase in load on the engine, yet without killing the highway mpg that 4.56s would do, by up-ing the rpm at 70mph by ~500rpm. When you did down shift on the highway to 5th, the jump would only be about 500rpm, compared to the stock 800rpm (5th to 4th). The 4.88s on gears 1 thru 4 would definitely give some better acceleration.
As the OP highlighted, getting the electronics to play nice will be the hard part. If anyone has some feed back or ideas, I'd appreciate it.