I installed a used tranny for my 1993 F-150 Flareside. I have slipping in 1st gear at first start up in the morning. After a few minutes, it does not slip anymore. However, when I am on an incline at a stop, and then start to drive, I get an in and out of gear slip and it tends to cause my gear changing a bit out of sync. Anyone got any clues on this?