I'd be surprised to find a 2.91 in a rig like that, I'd expect min 3.23 - that's what the one I tore apart had. And they're no speed demon nor stump puller but they'll get along. They really seem underpowered compared to the new computer controlled stuff that does so much more with so much less displacement, but for the original times, not all that bad. Just my opinion...........
I would guess that is with an automatic transmission with that high a gear. It would help get rid of some sluggishness if the 31s were traded for some 28s.