need help! I don't know nothin' about gears!

Put an 8 3/4'' rear in it with some 3:91 gears and a sure grip and it will be a different car.
It's not the little rear end's fault, it's the highway gears and the lack of a sure grip.
The 7 1/4'' in it is too wimpy to last if you are going to beat on it much longer.
The 8 1/4'' is good for a street application, but you say you are going to run it at the strip, so i would go with an 8 3/4'' seeing that you are starting fresh anyway.