Iffy A/C just stopped working when stop?

[Truck Guy99]

Truck is an 05 Chevy Silverado 1500. About 6 months ago the trucks A/C shut off when you turned the fan speed to 5 but would blow very lightly on 0. All fan speeds between worked fine no matter if you were moving or sitting still. This was never an issue so we just dealt with it. Now when you are sitting still it won't blow at all no matter what you turn the knob to. When you start going down the road, it blows but barely. The air is very cold when it does this. We replaced the A/C fuse and the resistor that I'm told is common to fail and neither changed it or even made a difference. Could it be the climate control or is it something else? I'm in the middle of a Texas summer and need A/C!