Erratic Starting problem in 96 Jimmy

Hi All
I having some trouble with my 96 Jimmy. (4.3 l. Vortec)
The first start in the morning (cold or not) is fine. The next start after that, the engine will "catch" for maybe 1 or 2 revolutions, then die. If I
then wait 20 seconds, then turn it over for anywhere from 5 to 15 seconds, it starts and runs fine. It doesn't have any predictable pattern, except it always starts no problem in the morning. After that it is hit and miss, with maybe a 40% chance it won't start the first try.
The trouble did start after the fuel pump was replaced, so of course that's the first thing I checked. The fuel pressure, both the prime and the running, is exactly where it should be. (I haven't caught it not starting with the pressure gauge on.) I'm running injector cleaner through now, but there doesn't seem to be any improvment after one tank.
I don't know if it's related, but maybe it will twig something in someone, but the gas gauge is also reading incorrectly now. (Reporting 1/8th when dry... luckily I was only half a block from the gas station!)
The truck runs great once it has started, no lag, no roughness, no loss of power.
I'm stumped! Any suggestions would be greatly appreciated.
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If is a HO vortec (WOTH OUT carb looking device on the engine) then you may waht to check the fuel pressiure requlater under the ait plemum. this part is attached to the fuel injucter or the 2 6" long fool linedunder there as well. Pressure reg ( attached to injector) $450 Fuel lines $67

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