What does a Selinoid do?

I have a '95 Grand Am with 134,000 miles. Lately when climbing long grade hills when in cruise mode at 65 mph, my car seems not to be getting gas and the car goes into overdrive 2-3 times. I have had a new oxygen sensor installed, a new fuel filter installed to no avail. Then a new set of plug wires were put on and I was advised that the selinoid might have been damaged but to continue to drive if no problems. Well, after three-four days, the same problem. Is it the selinoid?

Do you mean a Solenoid? A solenoid is simply an electromagnetically powered plunger. In other words, it is a rod, attached to a magnet suspended in a coil. When the coil is energized the rod pushes out. Well, not exactly, but something to that nature. In your case the solenoid would be the part that actually activates the throttle body, regulating speed. If for some reason the solenoid could not push all the way out, not allowing the throttle to open completely, that may explain your problem. Then again, maybe not.

check you air filter too. i can cause you car to run bad.. going up a hill you car will drop to 3rd gear and back to overdrive. its just to keep your speed up.