GMC Repair: Fuel problem, gmc vandura, volume test

Question
I have a 1988 GMC Vandura with 66,000 miles on it
and it was running like a top until 1 day I stopped to get gas and got about 2 miles from the station and stopped at a red light and the van stalled from out of nowhere (it had never done this before)so I got it started and took off
but it was running very rough.I got it home and bought some B-12 water seperator,put it on top of the 12 gallons I had just put in there and did not help,then I replaced the fuel filter,no good.Then I replaced the dist. cap and rotor,nothing.I pulled out a couple of spark plugs to check if they were ok and they were,so
now I am thinking my fuel pump is going out(by the way it is getting fuel to the throttle body but I think the pressure is low)I am at my wits end and dont want to replace the fuel pump (since it is in the tank)unless I am certain that, that is the problem.what is your insight on the matter? I would very much appreciate your input before I go through the trouble of changing out the fuel pump.Thanks, Eric  

Answer
Hi Eric. The first thing you really need to do is take a fuel preasure AND volume test and make sure it is to specifications, until you do this I would not put anymore money for parts into the vehicle on a quess, It could get expensive. If the preasure is low, you will need to disconnect the connector for the fuel tank and make sure you are getting battery voltage at the gray wire while cranking the vehicle, also check and make sure the black wire is a good ground. Get back to me and let me know how you made out.