Am/fm reception sucks.

Ok, so here's the deal. I'm running in a company owned 06 379 Pete w/ factory am/fm. And unless I'm within 25 miles of a major city, radio signals last about 5 miles. It has satalite radio capabilities, but if it's one thing I do't need, is another bill. So satalite radio is out. I've also been told the am/fm antenna coaxial are joined in some sort of junction box with the cb antenna coaxials, is this true ? I'm at this point believing truth to this as I see no external antenna (am/fm) on the truck.
I have removed the companies CB and antenna system and installed my own as there's sucked also. And I did find that if I put one antenna whip back on the radio reception as better, but nothing to write home about.
So I guess what I'm looking for is without tearing the truck apart (which I have very little time for) is there truth to this coaxial junction box ? If not, what can I do to increase the radios reception before wade the truck up screwing with the radio dial ?
Oh, and I also have been using my smartphone as radio, but thats not helping my cell bill any, and I don't believe it's doing the phone any good either.
Sorry this was so long and dawn out, but I tried to give as much info as possible to avoid questions on your part.
Thanks,
SCJ