w4ho computer/gear issues

i was talking with my friend who used to race camaros, he did it for a while, and he was telling me about the 1st time he raced an 88 iroc with the computer in it, he told me that when he was switching gears to 3.73's he only got 4 tenths of a second off, and that he knew something was wrong. He said the computer on the camaro didn't really recognize the new gears, and he had to get a handheld tuner and fix it. Im wondering if any of you guys have experienced this with mustangs? i have a 95 gt, and i want to get some FRPP 3.73 gears installed, and the install costs are allready pretty steep, don't want to have to the buy the handheld tuner now, i would down the road, but don't quite got the $ now.

EDIT: My car is a 5sp manual!

no, im not talking speedo, you know if you have an AODE car, it still thinks you have the higher gears, so it doens't shift correctly, but since mines a 5 speed it shouldn't matter because i control when i shift, i just wanted to clear this up before i chat with him tomorrow! thank you though, i was hoping their was no comp tweeking i've had to do for just a gear install.

allright, i think he misheard when i told him manual, cuz he asked me and i said manual and then he said o ****, then in that case you need to work on the computer etc. Ty for clearing this up i just want to have my ass covered before i make this purchase.