M 1028 loosing power.

[beltfedonly]

Starts and idles fine, starts loosing power around 45 miles an hour. Just started doing this. I figured it may be the fuel filter so I changed it, could not get fuel up to the fuel filter. I replaced the lift pump and instantly got fuel to the filter. Trucks starts and idles fine but feels like it is running out of fuel at road speed. I have read most of the post about similar issues but thought someone may chime in with a suggestion.
Beltfed

 

[doghead]

Bad IP.

 

[cpf240]

Is the check valve on the IP clean?

 

[beltfedonly]

Cleaned the check valve in the IP, wasn't really dirty. Figured is must be the IP, so was reading up on how to change it. This morning just on a whim I pulled the rubber hose of the inlet side of the lift pump and blew air through it at about 7 pounds, could hear the fuel in the tank gurgle, truck now runs fine. Temporary fix but now I know it is not the IP! Will drop the fuel tank when I get a chance. Hope this helps someone else that may be having a similar problem.