i have 94 ls motor in my 92 dx hatch

i have been using the stock ls p75 ecu but im starting 2 see problems after a 8 months ago after electronics teacher installed skunk 2 chip off ebay that fucked somthin up: lemp home mode at 3000rpm an ac stayed on

i got the chip removed a day later an i had 2 put a switch on my ac and since then ive never payed much attention til after the swap from my totaled 94 ls to 92 dx hatch and i upgraded 2 a 2.5in full exhaust- it back fires when i change gears an when im take my foot off the gas around 5grand
it did this in my teg after the chip was put in aswell i just notice it more n the hatch cause of different exhaust

i heard stock ls ecu goes 2 bout 7000-7200rpm an my untuned safcII says 6900 at the red line


im tryin 2 get a new ecu an i know p28 is vtec but i can still use it just wit a check engine light
will it really hirt anything on the motor an what is the redline on p28