As I have stated before, just my opinion, but the 21G tongue weight is too much for most half ton trucks. I was looking through the 2013 Ford Towing guide that
JCZhome linked and found on page 24 for the F150 Max TW is 1320 lbs. So I looked up the Towing guide for the 2020 F150. It lists max trailer weight 13,200 lbs.,Max payload 3230 lbs. and max TW 1320 lbs. (for a properly equipped truck). Why only 1320 max TW with 3220 lb. PL?
I don't know the answer but I suspect it has to do with the class IV hitch rating.
It got me to thinking about the hitch rating on my RAM 2500. Couldn't find it in the owners manual or on the hitch so googled 2012 RAM 2500 towing guide and found in the small print at bottom of the guide. Class IV, Max TW is 1200 lbs. for 2012 RAM 2500.
I knew my hitch was sorta wimpy. Flexed a lot. Weight sheet for my 21G said TW was 1152 lbs. when left the factory. That's not counting the two
full propane tanks, two batteries, 1400/14000 equalizer hitch and that I only dump the black and grey tanks about every four days when traveling. Have never weighed the hitch but might be pushing 1500 lbs.
I've towed my 21G over 4,000 miles and the hitch hasn't failed yet but just for peace of mind I ordered a bolt on class five hitch from etrailer.

So my advice for anyone thinking about a 21G, 25G or 28G, check you hitch rating of your tow vehicle before you purchase.

Larry