Your story is similar to mine where I started with a Tacoma towing 5,000 lbs to a Tundra towing 7,000 lbs to a GMC HD towing the same 7,000 lbs, with a 14,000 lb 5er in my future. Seems like a natural progression.
The Tundra is rated for 9800 lbs, but I would not want to tow much more than 7,000 lbs with it. The HD (rated for about 4,000 lbs more) was definitely the way to go for me as it made those longer trips a much easier and relaxing drive, and it will look after any upgrades that might come along later. The difference in towing experience is amazing, and I'm glad that I made the move.
Tough decision to make for sure