johnny silverado

ok everyone, im new to this but I need help so this is where I decided to come. I have a 95 chevy Silverado with a 5.7 350tbi. it was sputtering and surging really bad and it had a terrible exhaust leak by the manifold. so I replaced the whole exhaust with true duals with hedman hedders and magnoflow xl mufflers. I didn't reinstall the o2 sensor and it still ran the same. I bought it with the exhaust leak and it ran great but it got worse and I figured it didn't have enough back pressure and it was due for an upgrade. but anyways the sputtering and surging continued. it also would die when I try to come to a stop unless I tap the gas as a break to keep it from dying. I just got the o2 sensor welded back on and it runs a lot better than it did but it still runs like crap. it used to feel as if it was going to fall on its face everytime I stepped on the gas until I got going but that stopped but it kind of accelerates really bad and it dies when I come to a stop and sit for a couple seconds unless I tap the pedal. also I checked the engine lights and it threw me a couple codes: 13 15 22 33 44. I know what these codes are but I don't know which one to tackle first or if they matter. im just looking for some guidance. please and thanks.