1995 Ford f350 351stumble

I have a 1995 ford f350, 351 Automatic, direct injection. I am having a stumbling problem. Starts fine, idles smooth. When I give it gas especially under load it will stumble. When I take the load off when I pick up speed a little it will smooth out till I put a load on it again. Also the overdrive light seems to blink when this occurs. I drove it all day yesterday after sitting for A MONTH and it ran fine till I ran it today and the problem started this morning after a short distance. Some times when I tromp the gas pedal after I get up a little speed it will take off. When I power brake it it will shudder or miss. When I let go back to idle with in seconds it will go back to smooth idle. I changed the fuel filter a couple months ago, It seemed to be restricted. It ran fine for a while then started again. Before I changed the filter I added Lucas fuel injector cleaner and dry gas in each tank but have refille the tank since then. Any thoughts would be greatly appreciated. Thanks, Phil