1999 GMC Jimmy 99 Jimmy Won't Start

Engine Mechanical problem
1999 GMC Jimmy 6 cyl Four Wheel Drive Automatic

I have a starting problem with a 99 GMC Jimmy. First time: sitting in a parking lot, would not start. Turned out that the 10 amp fuse for the cigarette lighter, PCM, etc was blown. Replaced the fuse and it ran well - for about a week. Next time: sitting in the driveway, would not start (had not been giving problems, no lights, etc). Fuse was fine, but no fuel pump sound at turn-on. Replaced fuel pump. Still no starting. It would run when I put gas in the throttle body, but only til it used that up. Replaced fuel filter. Still no pressure up to the engine. Replaced the oil pressure sensor, but got a 1345 code. Realigned the distributer and that seemed to fix it. Started and ran it for a couple hours, no problem. Ran it around the neighborhood, no problem. Drove it to work (25 miles), with no problem, but it did have the check engine light on. Was not sure if the codes cleared themselves, or a dealer had to do it. But now it will not start again. Fuse is fine, but I am at a loss where to check now. It has a new fuel pump, filter and oil pressure sensor - any ideas?

Update 27 Dec 09:
The check engine light had been on a couple days ago while the 99 Jimmy was running, before it decided that it did not want to start again. I checked it today with a scanner, and it came up with a trouble code of P1404. Since I was not near a computer at the time, I could not check the ID of the code but it read: "Manufacturer Control, auxiliary emissions control". I cleared the code and scanned again. It came back with no codes found. But it still would not start. From there, I checked the fuses, the fuel pressure and the fuel pump power lead. All fuses appeared good, tested with a test lamp. There was no fuel pressure at the relief valve. There was no power running through the gray wire that provides power at the fuel pump.
I was told that the PCM would not generate a trouble code unless the engine was running. So I poured a bit of gas into the throttle body and started it. It ran for a few seconds each time. Still no new codes were generated.
So apparently the code P1404 is a make-specific trouble code indicating either 1) the Idle Air Control Valve is fully extended, or 2) EGR Valve CKT performance actual pos. Greater. Looking up other similar posts pertaining to these valves, it seemed that they would cause rough running, but not prevent it from starting. It seems that cleaning them would be a first step, but what next?