My 1995 F-150 slips out of first gear when starting out in first. However, it doesn't do this at any other time. When I come to a stop and allow the truck to slow by using the transmission and finish slowing in first it doesn't slip. Only when i slow down with the break and make the shift from anyother gear to first while keeping the clutch pressed the whole time. Then try to accelerate again it will slip. any thoughts?