It could very well be an antenna problem. If it was already installed, it is possible that the antenna is not securely fastened in the rear of the unit...or the factory antenna is not working.
Can you manually tune in to the stations you desire? Also, check the "local" FM sensitivity settings to make sure it's not bypassing all of the other stations when not manually tuning in to stations.
Lastly, is your truck tinted? Certain tint is metallic and negatively affects the vehicles radio reception.
Regarding squig's comment above, I agree that this unit is not one of Pioneer's best, but it's far from the worst. I self-installed the unit and enjoy crystal clear reception of both AM & FM stations in my '06 Impala SS. Also, regarding the fact that he has illumination & speed sensor issues, and faulty GPS tracking, he either got a sh***y install job, or a bum unit (or both). The illumination issue is generally related to the OE compatibility & wiring harness, and the speed sensor is rarely a plug-n-play -type connection. You need to dig into the OE wiring to connect to it. That speed sensor wire also affects the GPS tracking/positioning for the unit...however, the unit self-adjusts to make sure you're always driving on roads.