Alright gents, as soon as i fix one problem another one pops up. I have 92 f-250 custom 5 speed with a 7.3 IDI. The problem first started today on the highway while i was driving to work and went to shift into 5th gear and she acted like she didn't want to go. I eventually got her to engage into fifth, but when i was coming off the local bypass and started down shifting to stop I couldn't pull the truck out of second gear. I eventually got it out but it took a bit. A little further down the road i came to another dead stop, but this time she wouldn't engage into any gear. I was stuck at an intersection waving people around me. I eventually got her to enage into third and eeked my way out of there. What do you guys think. I think my slave valve might be bad??????

 

First thing to check is the fluid level in the master cyl resevoir. If low check for leaks. Look under the dash at the pedal linkage for any signs of fluid at the firewall, if any found replace the master cyl. While there check for worn/broken bushings in the pedal linkage.
Fortunately you have an external slave cyl so check for fluid leaks there.
Also check around the firewall where the master cyl bolts on for any signs of cracking/flexing of the firewall when the pedal is pushed down.