Thanks for the question.
Sounds like the governor is sticking or the sealing rings in the back of the case are grooving into the case.
Thanks
Fordanswerman
FORD MOTOR COMPANY CAR AND POWERSTROKE SPECIALIST FOR OVER 16 YEARS. ASE MASTER SINCE 1991. CURRENTLY WORK AT A MAJOR FORD DEALERSHIP. GIVE ME YOUR FORD PRODUCT QUESTIONS, IF I HELPED, PLEASE HIT THE ACCEPT BUTTON. EXPERTS QUESTIONS ON FORDS WELCOMED