What causes my 1991 f150 to run fine until I shut it off for 5 minutes then run rough on restart?

Fuel draining back into the tank with little or no residual pressure for a restart - but usually, that's hot and cold. A fuel pump that's getting old, warming up, and loosening up in it's windings (kind of like an old starter would do). A fuel injector that leaks down. An ignition module that's getting ready to go. There's only a partial list. It's going to take a little digging. A few more details from you might help - engine size, continues to run rough or clears up, smoke, Check engine light, etc.

raw fuel trickle to intake, percolating fuel bowl carburetor,,,leaking injectors if fuel injection ! as said one of many, most likely

Your vehicle is twenty-three years old. The oldest one I have was made in '51, then I get newer beginning with 96's through 2010. Some call me anal, but I replace easy serviceable parts just because they become old. The injectors on the 96 are replaced every seven years. Yes they still work, but they are old. Same goes for waterpumps, alternators, distributors, coils, battery, etc. I find it preferable to schedule these chores at my convenience to standing on the side of the road with my cellphone calling Triple A for a tow back to the abode.