What could be wrong?

I bought a 94' ford mustang V6 3.8 L Manual, it had 179,000 about a year and a half ago. On a trip home from Las Vegas, the water pump blow and it over heated, cracking my head. I pushed the car back and poped the cluch and it started I made it home and then that night my ex put laundry detergent in my gas tank. We had the engine rebuild and it has ran like crap ever since it now on the bebuild has about 12,000 miles. The check engine light just barely turned off, on its own. We have replaced all the sensers. O2, TPS, MAF, Fuel Filter, Air filter, Spark Plugs, Spark Plug Wires, thermostat, the clutch, coolant tempature sensor. But we are still having a problem. When you start the car it sometimes will die, but most of the time it will bog down and rev up. When you drive it once you hit about 2-3000 RPM's it will studder, almost as if it was running out of gas and it doesn't stop until you put the car into N or until it is over 3000 RPMs. I don't know what else I have to do to get it running right. Once it is warm it kinda struggles but it runs alot better. Is there any hope for my car?