1993 Mazda MPV runs really rough once warmed up

Engine Mechanical problem
1993 Mazda MPV 6 cyl Two Wheel Drive Automatic

Mazda mpv 1993 V6 JE, 1. Started running really rough and than stoped and would not winde over. 2. Mechanic told us it was the module in the distributor so we brought a new one. 3. Starts, but now you can drive it till it gets hot and than it drives REALLY rough again, The muffler was even glowing red. 4. Mechanic put new distributor cap, rotor button and the coil, and still doing the same thing. Its has been at the mechanics for 3 weeks and still they dont know what the problem is. My problem is I have 4 children under 5 and no car. I am really need your help on solving this problem. PLEASE