When Iam driving it will just start back firing and it will keep on doing it till i let off the gas and aply in once more but when iam driving and i punck it it will do it and i was told that it was my spark plugs but when i put theme in itdint do it and then the next day it strated it agin so what is it??

Optional Information:
1995 Chevrolet silvrado 5.7L

Already Tried:
spark plugs