I have a different situation, but in your case your max tow is 7,900 to 8300 lbs. That is way more than you old nissan. The added weight of your truck should make it feel alot better to tow. You can always down the road change out the rear end gears to a 3.55 or a 3.73.
You should be fine for now. It's only buyers remorse, don't let it eat you up inside. Run with what you have now and like I said you can all way swap out the rear gears later on.