2000 mercury mountaineer rear leaf springs needed 235,568 miles

[Summajet]

I replaced my rear leaf springs on my 00 mountaineer awd 5.0L. I purchased Dorman leaf springs part #929-219. I have more sag than the oem springs. I looked inside the driver door jamb and under the spring code it had F1.
I tow a 6x12 enclosed trailer and a boat. What brand and capacity has anyone used? I have seen sd trucks springs i think they were 1250lb capacity each spring. I asked dorman what their capacity was and did not get an answer on capacity. I have seen some use Gabriel airjackers air shocks. I have read it is a bandaid fix for weak springs.
I would appreciate input on what others have used, capacity and less sag?
Thanks!

 

[RickOTR]

I recently installed some old man emu (ARB) leaf springs on my Sport and noticed an immediate improvement. No more rear sag, though a bit more harsh ride but livable. Did have to install new front/rear bushingsThe Dorman spring you are using have a spring rate of 1250lbs.

 

[Mr. Alligator]

I have had very poor results with other ”Dorman” products....

 

[Summajet]

Both Springs came with the front and rear bushings already installed.
What was the weight capacity of springs you had installed. It feels like it is lower in the rear and not as good capacity as the old ones. I had tied a piece of string on the hitch/touching the garage floor as a way to see how much it raised the rear. I got the string caught up on the jack and it ripped.
Anyways I am sure it is not the ideal situation but i have considered adding Gabriel Airjacker air shocks. Have either of you tried them before?
Thanks