Well, 9K# isn't too shabby, and the 6.0 has plenty of oomph, should be lots of options since plenty of manufacturers build light TTs. Still, it would serve best to stay well below towing limits, 5-6K# range would provide decent towing comfort.
We are on our 3rd Chevy Express 1500 with either the 5.7 and 5.3 engines and have towed our flatbed with several atv/utvs (about 3K#) all over the 4 corner states. We also have a Chevy 2500HD crewcab with the 6.0 and it did fine towing our 32' 10K# TT.
I have seen full size chevy vans towing RVs on many occasions at the campgrounds, most of course were smaller TTs as they did not have a 3500 with 6.0 engine onboard. Your well equipped Express is more than capable for many of today's lighter TTs.