Does anybody know approx. how much of a drop hitch I would need to get the ball to the height of a Chevy Avalanche hitch.

You may be suprised.
I took shank from my 2500 sub to 3500 dually and ball height was right on. Try it first before buying a drop shank.

I'm comparing it too my Chevy Avalanche though so I don't think it will be right but I will check first.

Just do like me! I brought the truck down / instead of a dropped hitch :).

Actually, the same flipped-over 2" hitch works fine from my last pickup. So, mine is actually a 2" RAISED hitch.

Yah ... I'll get right on that!!:D:D I like the stock look better.

I dunno, maybe try a tape measure?? :confuzeld