Ok, what you need to do in put the car in gear and then hold the brake and push the gas. This should put a load on the engine and you can reproduce the issue, there may be a problem with with one of the caps. There is just way to many variables, do you have any light that come on the dash, also if the car is computer controlled, look up how you can get the codes to display online, and then right them down and look them up.
many many different types of problem... do you lose power?
the last time my car was misfiring was when my ht leads were neally on their way out and before that it was my crankshaft sensor.
replace your dizzy cap [distributor], rotor arm, spark plugs and ht leads... they are all cheap parts and wont burn a hole in your pocket.
obviously you can take the car to a mechanic and have them diagnose the exact problem.
It should not start missing just cause you are going up a hill, you would have more load on the car. does the car use a carburetor or fuel injected, does it have a distributor or a cap per cylinder. There are so may variables with this.
You may have to replace your fuel filter. There is enough fuel getting through it for regular driving but when you push on the gas pedal and demand more fuel it may be collapsing a bit, not allowing enough fuel to get through.
No that's carburated because fuel injection shoots fuel in angle of car doesn't matter carburation angle matters cause it messes with air fuel mixture
Possibly a problem with the fuel line or the gas tank is dirty.
Its fuel injected