Why is this engine stalling after a short drive.  Feels like it is starving for gas.  Will start up after a while and usually no problem driving a mile to work and back.  Any further and it will stall out.  After it sits for couple of hours it will start up and drive  a short distance.  New fuel pump last year.  New Ign. control mod. 2 weeks ago.  Seems like it is getting fuel as the pressure is there when I push on the schraeder relief valve.  Mechanic had it when it was running and did diagnostic and couldn't find problem.  Ran for a while w/o problem then it return like a fury.  Someon suggested that it could be fuel pressure regulator that is bad.  Anybody out there having or had similar problem.  Please help.  

Had the same problem with a carburated small block. Is your fuel pump located up front or at the tank? I have a s10 blazer with 350 and had alot of problems with vaporloc. This is when the fuel boils (at around 80*f) and turns to vapor in your lines. If its hot outside, or your fuel lines run next to exaust pipes or next to hot block, it will boil. On my blazer I had a electric pump located up front and the exaust was 3 inches away from fuel lines running down the frame. fuel pumps wont pump air...

If you have a front mount pump, try installing it as far to the rear as possible and use a return fuel filter to keep constant circulation in the lines.  

I understand you were looking for someone that may have had a similar problem I don't know of any.
 However, it would be nice to know exactly what kind of blazer you have. I like your fuel presure test at the shrader valve, however you still may have a fuel presure problem even though you seemingly have good presure at the shrader valve, those things need alot of fuel presure to work. I strongly recomend getting a fuel presure gauge on it! that way you take guessing and assuming out of the equation.
Get that thing to stall then find out what fuel presure is at exactly, then test for spark, the 3rd simple cheap test I would do is shut the key off and then turn it to the run position and see if the computer does a bulb check with the check engine light while the truck is not starting of course.
If you gather that information I think you can get a better idea of what direction to go in. Keep in mind that if your fuel presure is low that doesn't automaticly mean you need a fuel pump, there is more testing to do at that point before you condem the pump. Likewise if the computer isnt doing a bulb check that doesn't automaticly mean you need a new computer, there is a ton of testing to do at that point.
 Trouble shooting the problem your having is gonna be time consuming and probably expensive. Your money may be better spent taking it to a qualified profesional with proper equipment. The fact that the issue is intermittent makes it a bigger pain in the A--. Maybe you could drive the truck till it's just about to stall and take it to your mechanic (assuming he is qualified), that way when he get's the truck hopefully it will stall right away and then he can do the testing and find out what is missing. You can save money that way because you won't have to pay him to drive it waiting for it to stall.
 Hopefully my input is usefull and apreciated. Let us know what the problem is once you get it resolved.  

stupid question but you changed the pump but did you change the fuel filter.if not change it.I know a few years the vortec 4.3 motor was having a problem with the spider fuel injectors under the intake.They also had problems with carbon hanging up the egr valve.You could try cleaning the valve.just a few this i have seen with those motors good luck.