1996 Chevy Suburban engine missfires, lacks power, exhaust n

My truck has started to run rough, it stalled out at a light, and since has givein me trouble, I took it to a mechanic and was told it need a fual presure regulator, so I had it replaced, it still runs rough, and misfires the mechanic told me it had a lot of fual in the engine from the leaking regulator, and thats why it was missfiring, there is a lot of black smoke, coming out of the exhuast, and there is a rattling noise in the muffler and catylitic converters, I hooked up a code scanner, and came up with three code descriptions, a random missfire code, a o2, sensercode, and a EGR valve pintle position circuit code, I replaced the distributor cap and rotor and the EGR valve, the engine seems to run better but it lacks power, at any speed, when ever I hit the gas pedal there is a poping noise and rattling from the converters and muffler, is there some kind of restriction from the exhaust cuasing the lack of power, or is there something more with the engine?