Tried mounting a CURT #13540 round tube class 3 to my 98 Eddie, 4.0SOHC, 4door, 2wd. No go. Hitch inside span is 41 and 1/8 inches whereas frame outer span is 42. Is the CURT actually wrong or is my frame whooper-jawed? Under vehicle looks good with no damage. Just wondering if this is unique...