If you will keep it another 11 years you may as well spend the money on the 14 when it comes out. It will be worth it to have the extra power and fuel economy. As you have learned life can change and having a little extra capacity in the truck won't hurt.
It seems the 5.3 in the 14 would give you plenty of towing power.
For what it's worth we have friends that tow with the current 5.3 and aren't happy with it. They are looking to upgrade.
I have the 6.0L in mine and it has less HP/TRQ than the 5.3 in the 14 will have. The 6.0L does a great job towing.