2002 F150SC and 5.4 auto and when warmed up idles at 1200 to 1300rpm. In the old days engines were tuned to idle at approx. 750 to 800rpm. Is this normal because my gas mileage stinks for a 4x2 which has been 13 to 13.5mpg. Ford dealer computer says engine is ok and has been given latest software update. Anybody out there that knows what the idle speed is supposed to be?

 

It's still in the 750 to 780 range +/- .
The PCM is programed with the base idle speed and references the crank sensor. The corrections to idle are made using the Idel Air bypass controller mounted on the throttle body, subject to any other sensor inputs that modify the idle speed on a temporary basis such as a cold startup and certain other times.
The PCM continiously adjust the IAC air flow to keep the idle steady by pulsing it. This part is not only a solenoid but is specially spring loaded so is has a controllable range of operation.
If your engine idles high after warm up and the dealer does not think it is a problem; shame on them.
The IAC, the Throttle body or possibly an air leak can cause the problem.
You like holding the truck, with the brakes, from creeping at a light?
Do some cleaning and checking if they won't look at it..