A quick rundown of the truck is a GM 14-bolt 1-ton axle and drum brakes off a 2000 Chevy K3500, front suspension and disc brakes off a 1980 C20 pickup, master brake cylinder off a 1998 GMC C3500,
Looks like you did your homework upgrading the right components.
GM corporate 14 bolt 10.5" rear axle/suspension is a very tough rear axle for serious commercial haulers or just pulling a RV. I made a living using them for several years when I was on the road. No more load than your carrying/pulling it should last for several hundred thousand miles.
I would be concerned with the lessor rated hitch receiver. Receivers and fasteners and mounting systems and the frame can also be modified safely for more load or draw capacity your using..... if done correctly.
