I have a Komatsu D37E 1989 that runs excellent except after about thirty minutes to an hour of pushing will start to bog and lose RPM. It wont stall as long as you quit pushing. If it cools down even for a few minutes it will be fine for a while and then do the same thing. Acts like it is starving for fuel. I have changed the filter and bled the system, no help... Any idea or directions on what to try next. Thanks
Run it for a little while whit the fuel cap lose, could be vacumm locked. There should also be a smaller filter in the fuel line.
The usual suspects are plugged screens in the tank or a fitting, a banjo bolt with a screen in it, random junk somewhere, etc. You could try blowing the lines back to the tank. Or tee into the supply line and run a line to a fuel pressure/vacuum gauge in the cab, that will tell you if that's the problem or not.