On the highway 33's are sluggish but bearable. Definitely will have you running mostly in the slow lane. As mentioned, aerodynamics are not an attribute of these rigs, so even the slightest head-wind will hinder you. Before I changed to 5.29 gears and replaced my carb, I ran 33's with a bad carb on stock 4.625 gears with my 2.6L engine at high altitude. Yeah, it ran like a dog on the highway, but if I'd had a good carb it would have been a bit better. With the new gears and a good carb I can keep it in 5th on most hills and accelerate in 4th. I spend most of my time in the fast lane now.

If your intent is to do lots of 4-wheeling then go with 33's, however, if you anticipate only occasional light-duty 4-wheeling then go with 31's. You'll get better gas mileage and highway performance with 31's.