You mention that it works for the "first ten minutes". What does that mean? The first ten minutes when the truck is cold (meaning coolant temp is the same temp as the environment)? Or do you mean the first ten minutes every time you turn the a/c on?

If you never turn the a/c on all day yet drive the truck until the coolant temp read around 190~* and then you turn the a/c for the first time — does it work for ten minutes or no?

What I'm getting at is what Little Caesar mentioned and that's the fan clutch. If the clutch is not working properly, the a/c would probably blow cold when the engine is still cold since the engine coolant temp isn't inundating the fan clutch's ability to cool the condenser. But as soon as the truck warms up to operating temp, the faulty/inefficient fan clutch is overwhelmed by the additional heat from the engine and the a/c will start blowing warmer air.

Just something to consider.

Also, when testing the fan clutch using all the normal test, keep in mind that though it may pass the tests — it can still be failing as mine was.