i bought this truck from a dealer , 12 Screw 4x4 , dealer put on some Dropstar 645b wheels 18x9 wheel. DSW645b8906818.

anyway I'm a family man , not big fan of these but the dealer put them on cause the old owner painted his factory and they looked bad. Should i be concerned about ratings or "offset" or anything like that? I'm a total newb in the wheel department and don't want to do anything that could possibly harm the truck affect MPG or most importantly have something happen when pulling a TT of 7000#. i pick this thing up in 2 days.

specs as per web are if it matters :bolt pattern 6x135/6x5.50, offset+18, back 5.71,deep lip 3.16,hub bore 108mm