Your GCW grew by about 18% by my estimates from towing your old TT to current one. 3.73 to 4.30 is about 15% better. So changing the gearing will accelerate not quite as well as your old TT.
Can you hold 5th gear now? Does it downshift too much? Or are you only concerned with low speed acceleration?
15% gear change will be noticeable. But will it be enough? What if you spent $2500 and still aren't happy? Will you want to spend another $15k for a diesel which is about the only way to significantly improve towing performance from what you have?
My recommendation: change gearing to 4.88. You don't need 2000ropm @ 80mph for non towing highway. 30% more wheel torque will be fantastic! You'll get over 3000rpm and into the powerband of the 6.2L much quicker in first gear. And you'll hold 5th gear much longer, maybe even 6th while towing.
