On-going fuel issue, 89 f-250 I6

[dustybumpers]

I have a fuel issue with my 89 f-250 I6,5 spd 4x4, and am stumped.


so far This is what I've done:

Check codes, no codes
new lift fuel pump in both tanks
new high pressure pump in the rail
all lines are good, no holes, or worn spots
new fuel pump relay
new ecm relay
new fuel pump relay wiring harness kit
new ignition module on the distributor
new fuel filter
fuel return transfer can replaced several years ago

I also have been from front to back in the harness, and all looks good.
All grounds are cleaned and good

what it does:
fuel pressure gauge is hooked up
cold start, 50 lbs, all is good.
removing vacuum source from the pressure regulator raises the pressure to 65 lbs, back to 45-50when vacuum is re-applied
as soon as the thermostat opens, the pressure starts to drop
the pressure continues to drop until the truck quits.
I can use a test light to energize the fuel pumps, but they don't build pressure


once the truck cools back down, it starts real hard, but it does start, then repeats the cycle.
any suggestions you can come up with would be greatly appreciated, I am pulling my hair out here.


Thanks

 

[dustybumpers]

I found the problem to be the fuel transfer can. It was full of sediment, and would not allow the fuel to be drawn, or pushed through it. $240 to the local ford dealer, and it's as good as new