It's real simple. Put it in high gear sitting still. Hold your foot on the brake firmly. Apply parking brake too it it's operational. Give it gas slowly watching the tach until the tach needle stops rising. The point the tach needle stops rising is your stall speed for that combination. But you have to have a manual valve body. If your transmission still shifts automatically, you will not be in high gear, you will be in first and it will not work.
