poor running

FILTER FILTER FILTER!!!!

Good trick .... farmers do this .... a NEW filter weighs a lot less than a filter full of crap.

Fill a new fiter with fuel then empty it out. Weigh it. After a few hundred gallons of dirty diesel from rusty jerrycans have gone through it, remove it, tip out the fuel, and weigh it again. In my tractor you don't need to weigh them - dirty filter in one hand FEELS about twice the weight a clean filter in the other hand.

Sounds like your filter can pass enough fuel to allow a LTTLE to get through and let the engine run gently but as soon as you deck the pedal to go up a hill the demand isn't there, and the injection pump doesn't get enough fuel through.

It may soon start drawing air and kill the engine.

Clean the fuel lines and fit new filter(s) !

If the lift pump is jiggered you may get the same symptoms.

CharlesY