2001 Dodge Ram Diesel Cummins

Hard start after sitting, will kill batteries after sitting
overnight it takes so much cranking.

Even when bumping starter to pre-run the lift pump
several times.

Disconnected hose at injector pump, ran lift pump, tons of fuel.

Once started, runs fine.

(I have installed a check valve before and after the fuel
filter, so fuel is not draining back that way.)

No evidence of fuel leak anywhere.

Very frustrating.

Any ideas? Thanks in advance.