Another option in the Keep It Simple variety -
LINK
You're never far from service, it's all interstate, no toll roads. Only two corners to document. Bypasses the worst of Memphis. I just rode thru there a couple of days ago, (heading to KS), and it's only mildly busy, no bottle necks. 24 hour gas is easy on interstate routes. If you leave at 4 am you're at the Memphis corner around 2 pm and back in Dallas by 9-10 pm. Heat is less of an issue right now.
The simple truth to LD riding is managing your stopped time. I.E. Stay on the bike. Speed doesn't help you and isn't worth the stress and additional fatigue. I don't know how you have the Street 750 set up. Hopefully some kind of wind screen. That reduces fatigue a lot. You should be able to drink water while moving. (and not from a bottle, from a 1/2 gal or larger source.) Ideally also snack from a bar bag or tank bag too. You want to avoid peaks and valleys in your energy and hydration. If you think about water, you need a drink. Some protein and sugar for snacks, low carbs. Have a sit down lunch when you're ready. You have plenty of time.
3.5 gallons. Do you have a comfortable 150 mile range at highway speeds? Or in other words, what MPG do you normally see?
Edit - Bring the NTTA tag. If you don't leave it on the bike, it won't get stolen. And you won't be leaving the bike sitting for extended periods during the ride anyway. Possibly not acceptable to you, but I drill two holes in the wind screen and run a zip tie thru the holes and around the tag, snug it up and don't worry about it. Makes it slower to grab, which eliminates the random impulse theft. Bonus, I don't have to worry about the tag coming loose when I hit a big bump.