I have a 350 tbi engine out of a 1990 c 1500 that is losing fuel pressure the warmer the engine gets the more the fuel pressure drops
it starts out at 10 psi when cold and drops to as low as 4 psi by the time the temp gets to 190 deg. I get the same readings whether the engine is running or not. I am using a new recommended gm external pump, rebuilt the regulator, pinched of return line and pressure goes way up.
seems to be lean at the plugs but dumping alot of fuel when running.

any suggestions ?