I am running 31" tires with my 5-spd and 5.12 gears (also have 4.24:1 TC gears but that doesn't come to play here). 5th gear is doable until you hit the grades. Here in CA, we have a small hill called the Grapevine where I have to downshift to 4th. Average speed is still 55 the entire way up the GV. We make this drive to play in Hungry Valley and the highway drive isn't bad.