Welcome to the group suchuster! The are several things you can reduce the heat in the cab, more than I'm going to type here. Here is the short list and you can do a search to see what's all been said about it.
1. Insulate the lines that run through the tunnel. You can also insulate the inside of the tunnel with heat reflective material.
2. Plug all the holes in the frame but you have to remove the fenders to do this one.
3. Seal around the fresh air intake tube under the hood. This is easy and makes a big difference with hot air entering the cab,
4. Run with the windows down and the front windshield cracked to it's first setting.
5. Close it all up and just run A/C
Insulating the lines in the tunnel and sealing the fresh air intake are the easiest to do and have the most bang for the buck. I would start there.