Sounds like you either have a wax build up, or you have a bit of a haze on the clear coat on the sides.
If your confident enough with your truck, you can wet sand your clear coat, and then buff it with a polishing compund and a rotary buffer.
Should make it shine right up!
You could try just buffing it first, though, because wet sanding can be difficult if you don't know what your doing. You could easily go right through your clear coat.
Mind you, you can do the same with just buffing, but you have a bit more room to play.
Good luck!