Hello and welcome to JustAnswer!
I'm betting you have an engine light on too? Maybe, maybe not. The a/c isn't cooling at a stop because there is no airlfow over the a/c condensor. When you are driving you get natural cooling, and when you stop the electric condensor fan should come on to keep it cooled and keep the high side pressure down. What happens on these is the fan motor will either get weak and spin very slowly, or it will quit altogether and blow its fuse (number 39 I believe), and when the fuse blows it will turn the engine light on. Most likely you are going to need a condensor fan assembly.
It will only come on when you have the a/c or defrost turned on and the truck has been running for a few minutes.
I double checked and the fuse is number 12 on your truck for sure, so we know it hasn't blown the fuse yet. Start the truck and turn the a/c on and let the truck run and see if the fan comes on, and if it does see how much air it pulls. You may not be that familiar with how much air these should pull if you haven't payed that much attention to it in the past, but it should move a good amount of air, comparable to what the engine mounted fan will pull. I believe you'll find that it's running pretty slow.
It may not pull quite the amount the engine driven fan does, but it does pull a large amount of air. If your a/c system has close to a full charge it has to be a condensor flow problem. The fan has been revised probably 4 times, and now comes as an assembly with the motor and shroud. It runs about $190.
You're welcome, and good luck!