idles like a hotrod but has no power

I'm completely at my wits end with this car. I got it a couple years ago with 120,000 miles, had to replace the master cylinder and the front passenger wheel baring right after I got it, but it ran absolutely great engine-wise until last month when it started over-heating. There was antifreeze in my oil, so I got my head gasket changed. BIG MISTAKE. After my engine got put back together, it took a week before someone could finally get it started and when they did, it idled like a hotrod and kept shutting off. I can finally get it to start right away and SOMETIMES it will stay running and be completely fine but other days, like most recently, I can't even get it to go 20 mph on a straight-stretch. I've tried getting a new TPS (Throttle Positioning Sensor) but nothing changed so I took it back and got a FPR (Fuel Pressure Regulator). My car still idled weird but it finally had power back again. That changed after two days of driving and ended up having less power than it had before when I could at least PUTT on the highway. At this point, I can't even drive it at all. Also, I've found that whenever it loses power, the underneath of my car starts smoking near my catalytic converter, a friend said it might be clogged and to check by drilling a hole in the exhaust in front of it. That didn't change anything either and now my car really does sound like a hotrod. It's not my coil packs either. It threw misfire codes, that my fuel is running rich, and my IAT (Intake Air Temperature) and MAP (Manifold Absolute Pressure) sensors have high voltage. Whatever that's supposed to mean? HELLLLLLPPPPPPPPPP ME PLEASE!