Help: Ignition Mystery!

My girlfriend's car is doing this:
When she's driving up this big hill on I-25, the car starts to miss and run like crap. It slows down from 75 mph all the way down to 40 mph...which is definitely not safe when everyone else is going 80. Sometimes it seems like it'll quit running completely.
As soon as she reaches the top of the hill, the car starts to run fine again.
Car starts fine, runs fine, everywhere except that very steep hill. I've put new spark plugs, new spark plug wires (good ones), new cap, new rotor, new coil.
Except for timing or a faulty advance, I'm clueless. The car is a 1982 Honda Accord with a carbureted 1.8. I know this isn't the right forum, but I really need your expertise and wisdom!
Flunky

fuel pump? If its happening only on an incline, I dont know why you would think it must be ignition.

I was thinking it was ignition, because first, I took off the cap and cleaned the contacts in it with some emery paper. The problem stopped for a week, then came back. I changed the cap and rotor that time, and again, the problem stopped.
What would cause the contacts in the cap to get fouled?
Flunky