Above lift will run fine, then after a while it will just sputter out under load and die like its not getting fuel. I have new filters, bypassed the lift pump with an electric unit sucking diesel out of a 5 gallon bucket to rule out the lift pump is bad- No change. Could the engine throttle actuator be bad?
The electric fuel on and off solenoid is very tempermental to proper voltage. We have a 40 with a Deutz and sometimes we half to put a booster pack on it to start, even though it cranks fast. I would check it for good voltage and anything else.
This will sound unrelated, but your alternator may be going bad. It will fluctuate voltage and that thing will do all kinds of stuff- shutting down is one of the more common things. You can put battery chargers,jump boxes and whatever on it, but if that alternator isn't putting out?- it will lay down on you. Good luck.