I would have to venture to guess that it is the tires along with other things. The tires on the Gator were larger and had a slightly more agressive tread. It could also perhaps be that when you lock the differential on the 6X4 Gator all 4 rear wheels pull. When the differential lock is engauged on the RTV both rear wheels lock, but only one front wheel pulls. Just a guess. I've no doubt that with a big run at this particular hill I could make it with the RTV, but I always just crept up it on the Gator 6X4. Again, for my needs I prefer the RTV and my concern is only with it not coming out of drive when I do not make it up a hill. I do not think a UT can be all things to all people. If I bought the RTV only for climbing hills I'd be upset, but that was not my particular need. Therefore, my only issue is the being stuck in gear thing.