Before you put down any money on a bigger TV, remember that a strong enough crosswind will flip even a big heavy semi. If it was my rig, I would get the true tongue weight and steering axle weight from a commercial truck scale and setup the WD correctly.
My TV/TT rig is very similar to yours - 3.6L V6, 30' TT, 7,000# tow, 12,000# gross. It is setup with a near perfect weight distribution. Last year I did a 4,000 mile trip through New England and had absolutely NO sway issues including going downgrade in the mountains at 70 MPH with a gusting 30 MPH crosswind while passing semis.