Tim (fab51), you bring up a very good point! Swamp coolers, or evaporative coolers, don't work well in places with high humidity!
Robslowchevy, you haven't said where you're from. In looking at your pictures, I noticed that you had Texas plates on your truck. Do you live in Texas? If you're in the East Texas piney woods or the Gulf Coast region or S. Texas, a swamp cooler will not be effective. If you're in W. Texas or the Panhandle, it would be ideal. If you're down here where the humidity exceeds the temp during the summer and you want to cool the cab, look into Vintage Air. You certainly have the muscle under the hood!
Ken