I recently bought a 1993 F250 with a IDI Turbo Diesel. It needed some work on the Brakes and fuel leaks. All the brakes, rotors, drums, calipers, booster, master and wheel cylinders have been changed. Fuel leaks fixed. I can tell I have vacuum, but the truck doesn't stop well. Hard pedal, but not much assist. I've checked the vacuum and after about 30 seconds it will read up to about 17Hg until you apply brake pressure and it drops to 4Hg and stays there. I just want to verify, do I need a new pump? Thank you.