1994 Ford Explorer

Did you do the clutch? Make sure the system has been bled properly otherwise it's likely the trans.

If vehicle had no shift problems before you did the clutch I would say keep bleeding.I own a Ranger that I did the clutch on and even the dealership laughed when I wanted them to bleed the system they said a lot of people run into the same thing and that they preferred to bleed the system as they made more money and it was less work. I ran into more a hard shift problem which finally was corrected after bleeding the system running the truck etc over and over.
The slave is part of the throw-out bearing and dealership wanted to charge me $400 to bleed that could have been because I didn't have them do the whole job.
Jumping out of gear though sounds like the trans the question is are you able to place the shift fully in third gear.
Check to be sure nothing is obstructing the shifter up top keeping you from fully pushing the stick into third and that the shifter is aligned properly.