What should I look at now

I have been having trouble with my 91 for a while now. It all started when I put a bottle of fuel system cleaner in. I began taking off and it moved sluggish and sounded like a machine gun. About 8-10 miles down the road It eventually just quit and I could not even get the rpms to move. I had to stop and wait a while for it to start again, then I would get about 3-4 miles down the road and had to repeat the process about 3 or 4 times until I got home. Now it can drive, but it is a little missy under 2000 rpms and does not have all of it's power. I pulled KOEO codes and got 15,33,15,33 pulse 85,96,85,96.I think this is way too severe to be a faulty tps or anything of that matter.
I took it to a mechanic and they say they don't know since they cant use the computer on it since its a conversion. They say it has spark and 35 psi of fuel. They say they don't even know what to start with. Some days the car will idle and never miss a beat, but it always drives like crap and other days the car wont stay running. I can't find any indication of a blown head gasket or anything like that. I assume the ECM, but I am not sure. They were complaining about stuff being unplugged but I know that it is all part of the smog system. I dont have any mods other than offroad exhaust and gears. If anyone can give me any idea on what else I should look at I would greatly appreciate it.

I know, but they said they checked when it ran and when it didn't, but Ill keep trying.