I have noticed for a while that my a/c hasnt been cooling like it should when stationary. It is better when moving, but still seems to take a while to cool and doesn't seem as cold as it once was. I have used a store bought a/c pro freon checker and it reads ok.

Any help/advice would be appreciated.

 

When the outside temps are hot, and you are at idle for a period of a minute or more, the A/C will be warmer; this is a known condition of these F150's that use a clutch type fan. Simply put, the clutch fan is unable to draw enough are at idle to cool down the A/C condenser that sits in front of the radiator. Ford did very good in providing a large radiator for the engine, so engine temps do not climb too high during idle, but the A/C suffers.
Many (myself included), have converted to an electric fan to compensate for this. The new F150's all come from the factory with electric fans.