Quieter in the cab?

[JAKES 68GMC]

How can I make my truck quieter in the cab? It's not too bad in there under 40mph, cause the motors just chugging along, but around 50 or so, its pretty loud. You have to crank the radio way up to hear it, you pretty much have to yell to talk to anyone riding with you, and you can't talk on the phone cause its so loud. Its not exhaust resonance, most of the noise comes right through the firewall. The 350 itself is a loud engine, its a lot louder than the V6 was with open manifolds.

Thanks for the suggestions of making my truck quieter in the cab guys, I appreciate it.