If adjusting on the truck, use a 1/2"-drive ratchet, suitable extensions and u-joint, and a barring tool to turn the engine and thus the pump... Check your PMs.

 

Tate was referring to tightening or loosing the two special screws that apply spring pressure to the Gov springs.
The screws turns about 90* then they make a click. Adding or loosing the screw a click or two will modify the rate of the gov springs and you should be able to fine tune this problem away.

I just adjusted some new 4 K Gov springs I installed in my '97 215HP motor. I turned the screw head out a couple of clicks to lower my upper end RPM range a little bit. It also will modify the idle point and how it revs.

There are a few videos on You Toobe that show that adjustment, but most just set it back to the stock location for that screw head.