miss and stumble like distributor or timing is off

After driving my 94 Ford Bronco for about 45 minutes, it starts to miss and stumble like the distributor is going or the timing is off. Changed plugs, wires, coil, distributor, cap, rotor, and had timing set about two years ago. Runs great up until that

Changed plugs, wires, distributor, cap, rotor, coil, and had timing set about two years ago.

Thanks :-)