With the engine off, have a helper slowly press the pedal to the floor and release. As the helper does this, watch the linkage, starting at the firewall.

You should see that linkage at the injection pump moves the lever from minimum to maximum as the pedal is depressed. Be especially on the lookout for the link that does not move, or binds. If the linkage does not move the IP all the way, figure out why not...

It may be as simple as cleaning, lubricating and adjusting the linkage.

Best Regards,
Jim