You folks recommending 4:10 and 4:56 rear end gearing have to realize the higher the RPMs you have to use, the lower the gas or fuel mileage you're going to get, especially using a gas engine. The fella with the 6.4 hemi engine is going to be disappointed pulling a fifth wheel trailer. The 6.4 hemi is an awesome engine, but he's going to be using high rpms doing it because the hemi engine gets its power and torque with high rpms. It's not designed for low end torque which is what is required for hauling big loads also, I remember back in the 70's, my then wife's bro in law was nuts about building racing cars and his car was a dodge hemi big block engine. He had installed 4:11 rear gears in it and one day I passed his wife driving it. She had the engine rpms maxed out and was only going 60 mph. His car was really quick off the line but top end speed really sucked. I said all that to say that 3:73 rear gears should be plenty with what he's got. My truck is a '99 2500 4X4 5-speed Dodge with a V-10 gas engine and 3:55 rears and I pull a 29' fiver. I don't have any trouble pulling 6% grades but I should have bought a diesel. A head or side wind catches that tall camper and really drinks my gas. I don't care how big a gas engine is, it just doesn't have near the torque a diesel does. This is all just my humble opinion and it's really none of my business what anybody does with their stuff. I wish that fella all the luck in the world, but I wouldn't do what he wants to do with a hemi. It's made more for racing than anything else. He could beat my V-10 in a quarter mile race, but I can hook on to the back of his hemi and pull him all over the place. I pulled a semi out of the mud a couple of times.
