Help!
 

I have a '93 F250 5.8L Supercab. From a stop, it occasionally wants to hesitate when accelerator is depressed. Additionally, it recently wants to cut off after it starts or randomly as I am going down the road. I put a code reader to it and it came back with an old code of oxygen sensor, which I replaced two years ago at the same time I had a new muffler system installed. A new code for a bad ground in the fuel relay switch also came back. After some routine maintenance items such as oil/filter change, air filter, breather filter, PCV valve, this is what I have replaced or done so far; new battery, fuel relay switch, plugs/wires, distributor cap/rotor and some new vacuum lines. When I got done this afternoon, it fired right up but after about a minute, the engine speed dropped and within a few seconds it stalled out. Any suggestions, please.