Interesting math...

To calculate drive ratios don't add the ratios, MULTIPLY the gear ratios: (in gen 1=) 4.652 diff x 1.944 tcase low = 9.04

So from a 35" tire to a 30" tire would cause your torque to be reduced by 30/35= 0.857x. To correct this, the diff would need to be changed to 4.652 / 0.857 = 5.428 diff gears.

For the basic gen1, the 28.5" stock tire swapped to 33's = 28.5/33=0.8636x, which would cause about the same difference as the 30 to 35 tire swap. And hence the popularity of the 5.29 diff gears: they correct the drive ratio back to "normal". CapnCrunch has done this, and he can move pretty good up the hills in Colorado with a 2.6L pushing 33's!

With the 4.3 swap, it works the same way, except that GM put the extra engine torque to good hiway use (in the original Blazer) by using diff gears of ~3.5, much taller than Mitsus. So in the Mitsu, with the 4.652's, I "gain" crawl ratio compared to GM, but at the cost of hiway low rpm cruising. It would have been helpful to swap in a set of say 4.22 Mitsus to help the hiway a bit, or even use 35" tires, as either would help the hiway milage. With the 4.3, 33" tires are a must in the Gen1's.
The loss/gain in torque with any of these diffs/tire combinations would not be an issue for the 4.3, but overall, I prefer the lower final crawl ratio it affords...


[/ramble]