I'm looking at a 2005 Silverado 1500 Crew. It has the Z85 suspension option, but not the Z82 trailering package. It's had a fairly substantial aftermarket frame mounted hitch installed, but it only has a flat 4 pin connector. It appears to be plugged into a larger round connector under the passenger side of the rear bumper. Questions... Is that round connector part of the usual 7 pin connector, or does it support the 7 pin connector that normally comes with the Z82 package? Is it as simple as adding a pigtail in order to add the 7 pin trailer connector? What else does the truck not have, since it wasn't equipped with Z82? Tranny coolers? Larger radiator? Other wiring harnesses? Brake controller wiring? I'm realy leaning towards buying this thing, but i want to use it to tow, as well. Don't want to be investing in a huge pain in the azz, or have a diminished capacity due to the absence of the "package". Any help will be greatly appreciated.