Who has switched from a '16+ max tow F150 to a '16+ HD F150?

As you already know the HDPP has heavier axles, heavier suspension, heavier shocks and LT E tires. Provided you were staying within rear axle rating and you already had LT E tires I would consider Timbrens which will provide additional suspension without impacting the unloaded ride and putting on some Bilstien shocks. That would give you a pretty good idea of how the HDPP would handle before making a large $ decision. I would run a good WD hitch.

Good luck,
Stu