Too much trailer?

The rear axle ratio is the least of your worries if you have the six speed transmission. It is easy with the six speed to pick a gear that gives you the rpm's you want at any road speed. Your real problem is payload with a relatively heavy trailer and a half ton pickup. You will hate driving an overloaded vehicle, no matter what gear you are in.

A 5.3 with 3.42 gears is not going to be fun in the hills of WV. Pulled a 9k 5er with my 5.7L Hemi for a while but had 3.73 gears and Michigan is relatively flat. I upgraded to a 2500 with a Cummins befor a cross country trip.

The only thing that maybe should have been changed is the rear axle ratio. It should have been a 3.73 at the least. The 3.42 will give you better fuel economy when you're not towing but when you're towing it'll feel like the trailer is weighing down your truck especially on hills. I had similarly equipped Silverado with a 3.73 rear and a small 5vr (gross 6350lb) and a 4 speed tranny. In order to maintain reasonable fuel economy when towing, I locked out O/D and ran it in 3rd gear and tow/haul all the time. In that configuration, I was able to maintain a reasonable 10mpg.

It would probably be OK for short flatland trips, but for longer trips, especially where mountains are involved, no way. What does the yellow sticker in the door frame say your payload is?