1995 5.0 runs poor when warmed up
 

1995 F150, 5.0, automatic, 121,000 miles, runs fine when first started after temp gauge reaches about halfway point at cruising speed the engine will start to bog down and you have to press accelerator pedal harder to maintain speed until finally trans will downshift and motor will begin to speed up but in a few minutes it will repeat the issue, when this is happening it surges at idle and when leaving a traffic light it is very slow to accelerate. The problem does not go away until the truck is shut off and cools down but once it warms up the issue starts all over again. Check engine light comes on but the only code is 565 for the purge solenoid. I tried unhooking the fuel tank vent line and blocking off vacuum, no different, cleaned MAF sensor, no different, unplugged MAF engine idled higher but ran no different. The exhaust is VERY hot and the fuel mileage has gone to crap, any suggestions would be appreciated

Hot exhaust? Sounds like a plugged converter.

When the motor is cold it will be in open loop. When it reaches operating temp it goes into closed loop - the computer starts governing the engine based on sensor input.
Does that sound like what's happening ?
I had a very similar set of symptoms when I changed my Y-pipe and the new O2 sensor was faulty. swapped out the sensor and the problem went away.