1994 firebird engine hesitation

Hey guys I am new to this but I am having some problems with my firebird. I recently had the catalitic converter replaced with a glass pack and I was wondering if I need to tune the engine again?

The reason i ask is because I have a problem with my engine that when I go to take off, the engine hesitates until I get over 3000 rpms. Since the converter went bad.... I just haven't had the same power I had before. I don't know if these two things are even related but the only other thing I can think that I did different was that I flipped a u-turn and it was done with the engine revved pretty high!!!

I am hoping I didn't screw up one of the cylinders and if I did, how much would it cost me to fix that.

This car is my baby.... I have had it for two years and it's awesome to drive, even though it's a V-6. The ultimate decision here is to find the problem without spending too much money.... otherwise I will just have to sell it.

I would try a tune up if it has been a while and then move on from there if the problem persists. Also how many miles do you have? and what year is it?