I recently bought a 1993 GMC C1500 5.0L with TBI. I had the radiator, power steering pump, oil pan, exhaust manifold and catalytic converter replaced by the local high school's senior automotive class. Before I took it in it ran pretty rough, but now it won't stay running more than a few minutes. I can't take it back to them because it is the end of the school year. It will start if I let it sit overnight and it will run (very rough) for a few minutes and then die. To get it to start after the initial start I have to hold the gas peddle to the floor. I've gotten codes 33, 34, and 54, cleared them, and gotten them again several times. I've already tested and replaced the MAP sensor. Before replacing the MAP sensor the exhaust was black, afterward it was white. The oil smells like gasoline and when I drained it I got about 7 quarts out of it. Can anyone help me?