Gear dilemma
 

Having a tough time deciding between 4.10 and 4.56 gears. I currently have 3.55s with 315/70/17, which are about 34.5 inches tall. Went tent camping last weekend and realized I may need to get back in a travel trailer. The one I am looking at is an 18 footer that weighs 4200 pounds. I will also be towing my four wheeler trailer behind that which is another 1200 or so pounds. Total of 5400 pounds which seems doable. The larger tires and 3.55s are overmatched so which would be better 4.10 or 4.56? My truck isn't my daily driver, so I don't do a ton of highway driving, but would like respectable highway mileage if towing at 65. Leaning towards the 4.10s now as I think they would be sufficient for that weight and the 34s. Thoughts?
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Depends on what sorta mileage u wanna get and how much you wanna feel the trailer(s) behind you when you take off from a stop. 4.10 would be a good match. You certainly don't need the 4.56's to pull your combo, but with your bog-me-down tires on there as well, you may prefer the extra torque when accelerating. All gonna come down to personal preference. Personally, I would think 4.56 would be a little too deep for most situations. Just my 2¢.

That's pretty much exactly how I feel. I drive like a grandpa anyways, so beating people off the line makes no difference to me. The 4.10s will suit my needs most of the time, where the 4.56 would be better for slower towing and getting up to speed. I get 14-15 mpg when not towing now and 13 mpg this weekend with a loaded bed and the four wheeler trailer, so mpg with the larger tires isn't bad, just don't want to screw up my transmission.

Just remember: a transmission is metal gears and clutch plates all working against gravity and Newton's 1st law to put your truck in motion. No matter how nice you are on the pedal, it will wear out eventually. Deeper gears only allow you to harness more low-end power. If you drive it as conservatively as you say, I don't think you need to bury yourself in 4.56's to achieve longevity. Use common sense: don't peg it to the floor under heavy loads, use gradual acceleration, and turn off OD when it makes sense. Unless you're towing very heavy loads around every day, I wouldn't think anyone would really need (or benefit from) such deep gearing.