mechanic didn't do a diagnostic check? he sounds like he is geussing with your $$$.
i would have a diagnostic ran on it and see what codes its throwing. then fix that not just throw stuff at it and hope its right!
09 XL reg cab
L4 2.3 , 40 series flowmaster , tinted windows 5% back 35% sides ,muffler removed from air box mod ,and ac on off switch mod , blinker mod, avs window vent shades
coming soon! k&n drop in/fiberglass bed cover/bed sprayed liner