Fuel Pressure Problems

[USArmyCombatMedic]

I have an 87 Chevy R10 350 and 700r4 4x4, its got about 80,000 miles on it. I have been working on this one for awhile and figured I would ask you guys for some help. So here we go...

My truck has been having some trouble starting up as in 10 or more seconds of cranking to start. It also likes to randomly die at stop signs. Not to mention occasional stalling while in gear at idle or shifting into gear (torque converter and tranny are both rebuilt within 25 miles). So I had a hunch that it was either fuel or ignition. Yesterday I hooked up a fuel pressure gauge up to it and found some answers. First of all, I threw the gauge tap in the line BEFORE the fuel filter. I know this is the least optimal location as it should be after filter or right before TBI however I was in a hurry. If you guys want or think its will be beneficial I will bend a new line to make the tap fit near the TBI.

The results, if I prime the fuel pump, (audible buzzing so it does work) the pressure will go to about 8PSI and then bleed down to zero within a matter of 5 seconds. It does not matter how many times I prime it, it goes to zero. The pressure while running is a constant 12PSI. I have a feeling that the PSI drops at stop signs or when I put it in gear which causes it to stall, but I will need a second person to help with that. The only thing new in the fuel system would be the tank (old one was rusted), lines (same problem), and fuel filter. I am fairly positive there are no leaks as I have replaced all the lines at this point. So what would cause the PSI to drop, and drop this fast? Please point me in the right direction! Thanks in advance!