Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
It is safe to use higher rated tires, you just have to make sure you inflate them to the correct tire pressure as the higher rated ones with often need more pressure then the lower rated ones that came on a vehicle so the tire pressure sticker will be wrong.
Many people upgrade to load range E tires to help increase vehicle stability while towing, the higher load range tires have thicker sidewalls that don't flex as much which in addition to added stability allows them to run cooler under heavy loads and it makes them more puncture resistant.
Some shops have strict policies about only installing the size and load rating that a vehicle came with but many shops do not have these policies and based on what you've said I think you'll be much better served by a load range E tire.
I hope I've been able to help you with your concern, if you have any other questions or if you would like more information on your current question, please feel free to ask.
2nd concern will stock rims be fine with 80 psi in them?
Yes your wheels will be fine, but one thing that is often overlooked is the replaceable rubber valve stems, standard ones are rated for 65psi a typical part number for GM trucks is 413, that's roughly 1.25" long, the high pressure replacement for this valve is 600HP, this valve stem is rated for a minimum of 80psi with some brands carrying an even higher rating. Most dealerships and tire stores will have these on hand but it's a good idea to specifically ask them to make sure that high pressure valve stems are installed, another option would be to buy a set online such as these from Amazon: http://www.amazon.com/Xtra-17-600HP-Tubeless-Snap-Valve/dp/B00ENRB7DU
Here's a link to Tire Rack's website where they go over the different types of valve stems and their pressure ratings: Tire Valve Types, Components & Uses