Why is my 94 chev prizem stalling and sputtering up hill

I would not go for throwing bucks to replace filter, or pump or gear box. Its a common problem with old car that has 'hot spot' built up in cylinder strokes. Mechanically its screwed up 'lagging or overlapping' timing problem. Means a requirement of changing engine. No point to replace engine for a car thats just margin to worth the labour cost and price of another engine (which replacemen engine you are not sure of if that has same problem with worn piston valves).Keep driving assuming it as disabled car unless you replace engine or get another car.

Hills are when you need the most power. More Power needs more gas and air than normal. Clogged air filter is easiest to check. Also check fuel filter, fuel injectors and fuel pump.