M105 looses power longer it runs

Has anybody had trouble with injector pump on model M105 XDTC farm tractor? It is at the dealer and they can't find anything wrong with the pump, but don't know why it looses power the longer it runs. It won't pull itself up a small hill, unless you shift down, and then not very good.

Sounds like a fuel problem which could be anywhere. If the filters are new, then have fun! Once I had a clump of fuzz like stuff in a banjo fitting that did the same thing. It took way too long finding that!

Thanks

Filters are new....read other posts of different Kubota's having same type of problem...seems like it is pretty difficult to figure out cause....wonder if this is just a Kubota problem, or if other manufactures have same problems?