It doesn't run

Dear Online Mechanic,
I purchased the 1986 Chevy S-10 Tahoe pick-up (2.8 L TBI V6), from an older couple living in a retirement community. The story they told me was, that it had overheated and blown the head gasket, and it was repaired, and had been driven afterwards, but for the last couple of years the truck had been sitting in the garage, because the old man had had a stroke and could not drive anymore. Anyways, I drove it off, I went and got it smogged, and it passed. I drove it for a while, and then I found out that the gas gauge was wrong, it ran out, I got it back home, everything seemed to be going well, and then well on the freeway it suddenly lost power, and died. It has spark, it has fuel, and it has air. I rebuilt the TBI, with no result. I replaced the map sensor, the throttle-positioning sensor, the oxygen sensor, and the Idle Air Control Valve. I got it to idle when I moved the throttle-positioning sensor out of specification, but it was running very rich, also, the map sensor was not connected. At this point, I am not sure what to do next. Any suggestions are greatly appreciated.

Thank You
James R.