1993 f 159 4.9 engine skips

Dear Guys, I inherited my great truck several months ago from my dad that passed away. The engine skips. and the check engine lite goes on after about 5 mins. I have changed the plugs,wires rotor,distributer cap,coil, vacum hoses, ecm computer and don't know what to do. After the battery is disconnected the truck runs great for a few minutes until the ecm resets. As far as I know this tells me that the injectors,and compression must be good or it wouldn't run well for a few minutes after the battery is hooked back up. The truck has 140,000 on it and is otherwise perfect. Please help. Kim