I have the Reese Strait Line WDH which came with the Reese 59740. IT worked well for my F-150. When I replaced the F-15o with the Suburban, I needed more drop like you and ordered the
Reese 63971.
If you need to buy a new one, then I recommend a 2.5" square vs. 2" and sleeve. Some people have reported excessive wear and towing instability using the adapter. I have not found a Reese Titan PN for similar drop.
Etrailer and Amazon Prime ship very quickly. If you can plan an extra few days of the TT in your driveway in the spring, you should be good. Local towing shops and RV dealers will likely have parts in stock as well, but may be more expensive than online.