Like truckracer said, you wanna inspect the dogs and slots on the sides of the gears for any abnormal wear. If it was only popping out of fourth, you may only need those two gears. Assemble your tran and carefully bench shift it through the gears, you have to turn the tran shafts and kind of hold things in place while your doing it. Look at what happens when you shift into fourth and fifth, you will see sets of dogs engaging with slots or other dogs. Those are the gears you will definitely have a close look at. If other gears sets are nice and square, leave 'em in.

 

Thanks. I will do that and get my baby back in action.