SBC 350 bogs and backfires under load
 

Hello, I recently bought a 1983 Chevy G30 class C motorhome, it ran great upon purchase. Last month took on a 2000 mile road trip into the mountains, it did great except for stalling at idle r/t elevation(5000ft and up). On the way back to Texas about 100 miles away from my North Texas home, it started to bog and cut out(pop) with anything more than tip toe throttle. I was able to limp home with problem getting worse with every mile. Fast forward to today and I still can not trace the actual problem. Noted a lot of things wrong when I dug in to spark/fuel. The distributor retaining bolt coupler was loose and it appears to have moved(changed timing), the bolts holding on the carb were not tight since they tried to float the to short of studs in the manifold. The spark plugs were oil fouled(the motor does not smoke). So here is what I have replaced; accelerator pump(edelbrock 1406), inline fuel filter, dist cap and rotor, spark plugs, spark plug wires, carb/manifold studs. It runs great at idle and with light throttle off load, starts right up no issues. Elec choke works as it should and is not closing under throttle. I can see the carb spray fuel when accelerator pump is activated. At this point I am at a loss, any ideas would be greatly appreciated. I am very mechanically inclined, but a novice when it comes to carburetors. Thank you in advance.