Ranger ('87) pu that stalls?

Sounds like you have a fuel pressure problem. most common fault of that would be the electric fuel pump which is located in the fuel tank. Being the vehicle is 20 years old, it is more likely that the pump is about worn out. I suggest you get it replaced as soon as possible so that it wont drop you on the highway. It is already giving you warning signs right now by stalling. If no mechanic was able to figure that out, I would suggest that you not go back to them ever again.