'94 Sable runs rough, stalls

[Jomamma]

I put a "New" engine in my car with 30,000 miles on it, after the old one got bad rod knock w/ 98,000 on it. Worked well for a while, then started having problems with it running. It was really hard to start, and it like to stall when you pushed it, but only after it had been running for a while. The check engine light has been on, it says that the coolant temp sensor and idle air sensor are both above max. voltage. For a while i just dealt with it, but 2 days ago it stopped running altogether. It stalled pulling thru an intersection, i pushed it into a parking lot. It started back up, made it a little farther, died again. did that 3 times then gave up. Before if you waited a bit after it stalled it would start up again, but you had to be careful or it would stall again. I think it might have too much fuel pressure??? I can hear the pump prime when i turn the key on, then when i turn the engine on i can hear it start priming itself again. all of this only happens after it stalls. I replaced 2 of the three sensors the computer said were above maximum voltage, they were only like 15$ a piece, and it still says they are bad.
Thanks for any help

[voip1]

For a 3.0L, there are two things that I would check first;

There is a connector to the body control module that is known for getting dirty. It is located above the radiator on the driver's side. There are two black ground wires that could be causing the problems that you stated (fuel pump relay in particular). By unplugging and replugging the connector, you may correct the problem.
Do you have consistant spark at the wires? If so, try some ether in the intake. If the car runs on ether, you have a fuel supply problem (see above).
I'd also be interested in head gasket condition. Does it over heat? Does it blow hot air out of the radiator when the engine is cold?