I would offer an additional item to look at... fuel pump.

I believe your engine has a mechanical fuel pump. I can equate your experiences with a 74 CJ (304) where I had similar issues until I changed the mechanical fuel pump.

Seems previous owner had rebuilt the engine but not replaced the fuel pump. For whatever reason the fuel pump would not deliver proper amount of gas under heavy load -- steady uphill pull.

I did replace fuel pump with noted improvement. However, due to other reasons, the engine was replaced and I did not have the same problem with the replacement engine so I cannot say for sure that was the problem.