Service engine soon light will not turn off

I desperately need some help please. I am working on my truck listed above with a 4.3 v6 engine and 117,000 miles. The truck sat for one week as I was sick and unable to drive. When I went to start it it would not start. I knew it was a leaky fuel regulator that flooded the motor. I put a set of plugs in it as I have in the past to fix the same problem still no start. At this point in time the SELS has never come on the entire time I have owned the truck. I had it towed to a local shop where my " buddy " changed the plugs cap and rotor and fuel regulator.
on the ride home the SELS comes on and the terror begins. The SnapOn scan tool reads a p0171 they said it was a bad MAF. They replaced it, didn't fix it.
they said it was the front two o2 sensors, replaced them, didn't fix it. Changed the air intake tube housing due to a possible bad gasket around the throttle body. Didn't fix it. Then they said it was a bad fuel pump, replaced that, the light is still on.I then had them take the intake back off to replace the regulator again in case it was a faulty one and to check they didn't have a vacuum leak. They smoked the intake two times and found no leaks. I didn't have a single problem until they worked on it, and the worst part is it runs great. Please help.
Desperate in Texas
Travis Lenk

PS: I also changed the oil to get any fuel that might have made it to the crank case.