IMHO, Best way to keep your highway gearing but go slower off-road would be to either change your existing t-case to a 4.7-1 crawl ratio or do dual t-cases.
Dual t-cases would mean driveshaft and floorboard modifications though.
Marlin has options for both.

Todd


1986 Pickup extracab longbed "Woody edition"
SAS - 33's, 5.29's, lockright rear.

02 IS300 SportCross - my "DD"
94 2wd v6 extracab
04 Outback Wagon- wife's/family car