Acceleration problem service engine light comes up?

Going back over 2 years ago I had a service engine light comes up and then flashing. Code reader displayed purge solenoid valve, evap, cat converter. I changed the solenoid valve, drained gas to check for water and was fine. Decided to installing new fuel filter. Put engine conditioner in gas and started using high test. Truck was running fine but if you steeped down its would not accelerate past 45mph. Kept driving it as no codes were present. Then started up 2 weeks ago and started running real rough at idle. Then got code po300. Said miss fire cylinder #3. So I decided to Change all spark plugs all ignition wires and coil for #3 cylinder. Started truck back up today after resetting code and runs ok it idle and in park I brought the rpm up and at about 4000rpm drops back off. Im basically back where I started from. Also back when I had the problem the fuel pressure at the rail was 65lbs approx. What do your recommend a the next cause of action. Im traumatized. I thought about taking the upstream O2 sensor out to see if with additional air flow it would give me a hint if exhaust is blocked from the converter but its impossible to get to and is probably frozen in place. Thanks for many input
Bob