computer question

i have a 95 firebird with a 3.4 i got it used with like 70k miles on it but it had aftermaket rims but no other visable mods but ive had the car going well beond the limits of the 115mpr speedometer i thought this was normal but i found several web sites that say this car will cut out at around 107 so i asked around and every one seed yes only ta's wil go faster than 110 without computer mods so my question is is this true and if so how can i tell if my computer has been modified

are the tires original size.. if so then i would guess there was some moding to the computer.