The hi volumn water pump may be your problem. The hot water from engine needs to stay in the radiator for a time to let the heat exchange process take place. I don't think the hot air in the engine compartment is your problem. You will feel that at the toe board and your a/c will work it's heart out to overcome it. One way to duct more hot air out is to build an air dam to force air from under the truck up into the compartment. Take a look at your modern car. I went one step further and punched two holes in the dam and ran two hoses up to the top of the compartment to help push the hot air out. Good luck.

Six volt guy living in a twelve volt world