Problems with car driving.

Hi Im new to the forum and have a question about the way my car is driving. I have a 1993 Pontiac Subird LE, with a 2.0L engine and approx. 105k miles on it.
Everytime my mother or I drive it, it stalls heavy. It' ok sometimes but gets worse the longer it's driven. It holds back like it does not want to drive. My mother and I replaced just about everything from spark plugs and cables, gas filter, air filter, oil change, etc. But it still acts the same. My mother recently told me that the reason it has been acting like that is because she just found out that my uncle put in one of the spark plugs wrong and now the engine has a gap in the hole where the plug was incorrectly put in.
do you think this could be the reason for my car to drive so poorly and if so is there anything that I could in order to correct the problem? Thanks in advance for the help.