721d loses power, stalls out

[BAchvytrk]

I have a grasshopper 721d with the kubota d722 3 cylinder diesel engine. Will mow fine for about 20 minutes then starts to lose power and will eventually sputter and stall. here is a list of what i have done so far
New fuel filters and lines
tank drained, cleaned, fresh fuel
Checked pick up tube from tank
new electric fuel pump
checked compression and valve clearances
injectors were ultrasonic cleaned
had injection pump checked out, they said delivery valves were bad, thought my issue was solved, put rebuilt pump back in and have the same issue.

i need some input, what am i missing here? i unhooked the fuel shut solenoid and the problem persisted.

 

[173abn]

check your gas cap vent to make sure it's not plugged...russ

 

[BAchvytrk]

thanks russ, already tried that too, just forgot to put in the original post. I'm going to try replacing the hydraulic filter tommorrow

 

[BAchvytrk]

no luck with new hydro filter. any suggestions? i'm about outta ideas

 

[173abn]

could you have a cracked hose that's letting air in,or is your fuel filter sealed tight where no air is coming in?...russ

 

[JUST4FUN]

Checked pick up tube from tank?? how did you check this ? what happens to our mowing crew is the grass gets in the tank and blocks the tube . We remove the tube and get a rag and hold it on the bottem of the tube and blow compressed air through the tube and a ball of grass comes out