Welcome to the forum, lots info here. The answer to your question is in the weight of all you carry. Every truck has a max cargo capacity as well as max towing capacity.
You will usually run out of cargo capacity first. You need to know the weight of family, toys, camp gear, and all the misc. stuff that get tossed into the vehicles when you are on the road. Then you can add the loaded trailer tongue weight. You are the only one that knows what your family cannot live without.
You are going to be spending big bucks for a new tow vehicle, so a guess will not do. You need an accurate weight and that means the CAT scales.
CAT scales give you an accurate weight on each axle.
Since you usually drive two vehicles. On you next trip, stop by the scales and weight your rig. Next weight the second car, empty people and stuff out of the car and weighs the car empty.
That weight difference is going to be added to your new truck.
All of the is a real pain to do, or you can guess weights and take you chances like most folks. Unfortunately guesses are rarely correct.
As for gassers or diesels it is mostly personal preference. I would not own a diesel but my neighbor loves them. He even ordered his zero turn lawn mower with a diesel engine.
I live where it gets very cold sometimes. Admittedly diesels have come a long way in recent years, still I want minimal hassle and expense when it comes to my vehicles.
Good luck
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.
Just right for Grandpa, Grandma and the dog.
