It's a "Heavy Duty Payload Package"... Not the so called "Heavy Duty TOW Package" which it often gets confused with..
F150's have several "tow packages" available thru the years..
Basically, if you get an F150 that has a factory installed hitch, that's considered the "tow package". From there, they have what is called the "Max Tow Package". Then they have the "Heavy Duty Payload package" which includes all the stuff the Max Tow has, but has a higher GVWR than the standard F150's.
In 2015 when they went to the "Beer Can" (AKA Aluminum) body style, they lowered the GVWR on them, but they still retained about the same "Payload" numbers as the prior gen of F150.
I have a 13 F150 that has the Max Tow option and has a GVWR of #7700 and a sticker payload of #1920. Has a #4050 rear GAWR and a #1100 tongue weight rated factory hitch. It's about #500 more than the average GVWR of the standard F150's of it's gen.
The 7 lug wheels went out after the last gen I think.. The 7 lugs were 10.25" semi float axles too. The new HDPP trucks with the 6 lugs are just 9.75" axle now, just like my 13..
Anyway, all the OP needs for his Dad is a Max Tow at most.. Those are fairly common compared to the HDPP trucks and would be more than enough.
Good luck! Mitch