1999 Chevy Blazer Blazer sputters and loses power on accele

There are no p codes that come up, only flashing letters, (C, O, EV, OH, E) I can start the vehicle fine and it will run while it is in park with no problems, but when I put it in drive after it has been running for a while then it will start to sputter, and I have no power it almost wants to stall but it does not. I can`t even get above 20 mph. But if I start the vehicle and drive it immediately it is ok for about 2 or 3 minutes and then it losses its power and begins to sputter and then I can`t get above 20 mph. I have tried unplugging different sensors and running the codes and then I do get a P number but that goes away once I plug the sensor back in. After clearing them I go back to just getting the letters flashing. Thank you so much for taking the time to help me with this.

Just curious if you ever found out about this. My 1995 is doing the same thing, and my mechanic cannot find anything to cause it. He changed the fuel filter, air filter, a couple of sensors, tested the fuel pump for pressure, cleaned the injector, etc, and he is stumped. Mine actually finally died as I coasted down the exit ramp on I-40 here in TN. I was going to trade her in last week, but now she won't run. Any help would be appreciated.