forget the dealer and the person you bought the trailer from. neither is your friend and only out to take advantage of you.
it's a good thing you didn't have an emergency, otherwise that 28' trailer could have easily overwhelmed your short-wheelbase Tahoe.:E
order an Equalizer WDH and a Prodigy BC from RVW. you'll get free shipping and your mechanic should be able to easily install it.
heck, you could install it yourself!!
my next suggestion is that before you venture out with the trailer, is that you educate yourself more about RV's, before you endanger you, your family and the rest of us.
the fact that you bought such an item without doing any research ahead of time, is something you can't afford to do again. you'll need to learn how RV's work and how to operate all the systems and how to get everything set up.