1989 Buick Century 89 Runs Fine Missing Drive Down Interstate Engine Just Dies

My 89 century runs fine with no missing As I drive down the interstate the engine just dies lik I'm not getting spark or fuel as I coast down the road when the engine just dies it starts right back up lik nothing I have replaced the ignition switch, icm, fuel pump, coil packs, map sensor, fuel pressure regulator, plugs, wires, air and fuel filters, computer, grounded the engine, keep in mind that the radio and all still are working when the engine stalls any idea what the problem could be please help