89 Cadillac Deville Backfires

Hi, im having backfire issue with my cadillac. Has a 4.5L V8 1989 year model. Before I replaced the exhaust on it I was driving on the highway and the car lugged down despite having my foot on the gas pedal, then all the sudden it starts backfiring excessively until my muffler exploded. I replaced the exhaust system recently it drives ok sometimes but it still tries to lug down. I dont know if I need a tune up, or major engine overhaul (camshaft). Where can I find a trouble tree? Or where would be a good placed to start diagnosing?
Please Help!:banghead:

Welcome to AF, you must start with determining engine is firing on 8, has proper fuel pressure, go to caddyinfo.com, ntructions on accessing on board diagnostics.