First, thanks for all your help and advice.
To recap, I recently bought a 2001 Dodge 24V quad cab long bed TD. I had a pressure guage installed on the lift pump to monitor pressure. It was installed between the lift pump and filter. It registered around 7.5 psi at idle (varied by +/- 1 psi or so) and would drop to 3, 2 or even 1 psi while under very moderate power (empty truck, not pushing it).
I bought a pump and filter (around $180 with tax) from Cummins.
Replacing the pump was not that bad a job. Using a furniture pad to kneel on, I used a 14 mm socket to remove the bolt holding the retainer for the intake fuel hose, a 17 mm ratcheting wrench to remove the intake and output hoses (being careful to save the gaskets!), then finally a 13 mm socket to remove the 3 bolts holding the pump. I had to use an 11 mm wrench to hold one of the studs as it came loose from the pump and finally it came out of the pump and a tiny vise-grip came to the rescue holding the stud while removing the nut.
Of course you need to unplug and reconnect the electrical!
Installation, the reverse of removal, went much more smoothly than removal except for losing the 8mm bolt that holds the retainer for the intake hose, but I bought another from the local hardware store so we are OK again.
I replaced the filter too as it was 15k ago. I filled the filter reservoir with diesel fuel and when I started the engine I maintained
2000 rpm to keep it from stalling (it did not try to stall).Now the pressure is 15 psi at idle and I cannot so far get it to drop below 10 psi. It seems my investment in gauges has saved me a $2k repair bill for the main injection pump!
So we watch the gauges and wait for the next time...
Charles