Chevrolet Repair: Fuel pump, fuel pressure gauge, consistant pressure

Question
I have a 1991 Having S10 84,000 miles. I started having hesitation and starting problems 2 weeks ago. I barely made it to a good repair shop and they told me the fuel pump was bad. I replaced it myself with a after market pump, with no change. I replaced the intake filter and inline fuel filter at the same time. I then replaced the fuel injector no change. i took it to another repair shop and was told fuel pump. I have replaced it with another after market pump, again no change. I purchased my own fuel pressure gauge and have found out the following. with gauge in the inlet fuel line I have 9# with the key on engine not running, the engine will not run unless I clamp off the return line to the fuel tank, with the engine running and return line clamped off I am showing 17#. I am being told by some that I should install another fuel pump but only a GM pump. What do you think I should do?

Answer
Hi Paul,

I suspect the fuel pump pressure regulator.  The regulator is a control valve in the return line system.  It pinches off the return flow to keep a consistant pressure at the injectors.  Just like your clamp did.  I cannot believe two bad pumps.  

If you have a throttle body, it is a large round object attached to the throttle body itself.  If you have port injectors, it is on the fuel rail.  

You should see 40#.  Less possibly with throttle body.  

Good luck

C J S