How do you correct the engine issues I'm having with a 2002 Pontiac Grand Prix GT 2dr 3.8L?

Catalytic converter is a no all around. As for the going up hill it sounds like gear hunting and its mostly something that happens in a pickup that's towing something. Its a case where the speed that you're going is putting enough of a load on your engine that the computer tells the trans to downshift to lighten the load and put more power to the wheels. After down shifting the computer sees little or no load on the engine and there isn't a request from the driver to accelerate so it shifts back up to save fuel. The process starts all over again. Try putting the gear selectorin a different gear like drive instead of over drive. The EGr won't affect the acceleration without affecting the idle. The need for a tune up could cause both issues but no guarantee.