I have a 1995 F-150 4.9L with a standard transmission. It has stuck in 3rd gear 4 times in the last 2 days and I do not know why. I am going to change the gear oil and I am trying to find out what kind of oil to use. The tag on the gear box has these numbers on it: F1TA GC A359905. Also what kind transmission is it and what could be causing it to stick

 

It's a Mazda M5OD. It takes Dexron III for fluid.

As for sticking in gear, it could be a few different things. Clutch, master or slave cylinders, or the transmission itself. These trannys do have a few issues with shift forks wearing out.