'21 4Runner left rear sag.

Afternoon,
I have a 21 4Runner with 50,000 miles on it and the left rear is leaning, close to a 1/2 inch.
I am 6'4' 300 lbs and would expect that only myself riding in the car would at some point cause the car to lean but not with it being 2 yrs old and 50,000 miles.
Worse case is that I replace the rear springs but so far unable to find some heavy duty stock (no lift) springs.
Any help, advice would be appreciated.
Thank you
Alan