Update 6/5/19. Added the biocide yesterday, a large shock treatment 1oz. to 10-15 gallons. Blew out the fuel line 10psi showing but did not drive to mix it up. Went for a drive, 0psi within 8 miles. Pulled onto the shoulder ( I spend a lot of time there these days ). Blew back the line and heard and felt a very distinct thud like a golf ball shooting out. Started truck 13psi idle, best so far. Drove 30 miles mostly around 65mph at 10 psi. Stopped at Napa and picked up some 5/16 and 3/8 fuel line, thinking that while the tank is down I may just replace the factory line that goes from a flexible section to the steel line as maybe that is causing or will in the future being 20 years old. Guess I will hook up the mechanical gauge on the dirty side again and check the differential since the Power Service fuel conditioner/slime remover and biocide.