If you will be trading any way. Go for the Burb. But unless you have a bunch of sway with the Tahoe. Don't expect a "World" of difference. After all. You will be using the same engine, and rear gear.
As for the Wheel base. The Burb will be a little longer. But if the TT pulls good now. You won't see any difference. I went from a Expe with a 118" WB to a F150 with a 145" WB, and honestly. There is no difference. Both tow rock solid, no sway, easy relaxed towing with both.
Terry & Shay
Coachman Apex 288BH.
2013 F150 XLT Off Road
5.0, 3.73
Lazy Campers