I'm running 265/75/16's and don't plan on going any bigger. The front tires when steering a tight circle are pretty close to the rear leading outside edge of the fender. I'm pretty sure if I have them chained and hit a bump at the wrong steering angle I'm gonna hear some unwanted metal on metal grinding noise. I may be looking at doing a little cutting and a bushwacker install.
The transmission hunting problem is the reason for the gear change. I don't push the van much past 65 unless I'm passing someone. The more I think about it the more I'm leaning toward the 4.10's. I gave up caring about gas mileage after about the 3rd full tank so that part of the gearing change equation isn't a factor.
If I end up doing the conversion I'll need to make the decision on which type of front differential to go with. I've already decided to use a Detroit Truetrac in the rear. The big question on the front is electro magnetic or air for the locker. I keep hearing stories about air locker failures. Pulled lines and compressor failures are the primary failure modes I hear about. I haven't spent much time looking into the failure modes for the E-lockers.
I just got off the phone with Aluminess and it looks like my front bumper and nerf bars will ship today. That install will take my mind off the gearing issue for at least a day.