Need more help

My '99 k2500, 5.7L "R" VIN, 98K miles, dies on me when the outside temp is above 100F. It acts like it is vapor locking, just dies going down
the road _or_ sitting at idle. I have to turn the key off, wait a few seconds (about 30 or so) and it will start up again then run for about a minute, die, here we go again....
While sitting in the parking lot the other day and sweating, I could hear the fuel pump make a "different" than usual whine just _after_ the engine quit. I don't let the fuel tank get below 1/2 usually, every once in a while it will go to 3/4 or so. It's hard to tell exactly because the fuel gauge doesn't indicate the correct level (about 1/4 low). Basically, with a 34 gal tank, I have never had to put in more than 25 gal.
I bought the truck used last fall, replaced all of the fluidsthe fuel filter, the fuel pump-cause it was dead (if I knew why, it may be a clue), just recently replaced the water pump and serp belt. I have one or two ideas about the cause, like the fuel pressure regulator?, or maybe a clogged return line? I've got the EASE scan tool software, it shows 105.5 mm/Hg for the fuel tank pressure (but 0.0 volts from the sender). This is the same with the gas cap on or off. No codes get set when it dies.
Thanks
Eddie
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i heard of dodges doing this and someone once said it was something to do with the wires to the fuel pump that in high heat they can lose the voltage so that the pump does not act right
Ed wrote:

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CTS = Coolant Temperature SENSOR. Not the one that feeds the gauge, the one that feeds the PCM.
Doc
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CTS (sensor) is ok.
Truck has been running fine lately, but outside temp has been less than 100 lately.
Doc, why check the CTS for a (maybe) fuel problem?
Ed

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the
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Ok, I understand the Open/Closed loop process. That is not the problem though. 02 sensors etc are doing their job too.
My problem seems to be with a fuel supply issue, but ONLY (so far anyway) when the outside air temp is greater than 100F or so.
Ed
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