I ran 31's on my 79 (4.10 diff with a 4-speed 22r) for about a year before going up to a 33. With the 4.10's I could still spin the tires in the dirt and keep highway speeds (highway being a relative term...I usually drive it around 60-65). I always had enough power to do anthing I needed (I also had 4.7's in the t-case). If it were me I wouldn't even worry about spending that much cash on gears for just 1" of tire...if your truck feels like it has enough power to turn the 30's it should still be able to turn a 31" without changing gears. Just my
