2000 F250 rear leaf spring replacement question.

I bought 6/1 springs last winter from SD Springs. My son and I changed them, but to be fair, he's a diesel mechanic and we did it at his shop. Took the bed off for easier access and used air tools. Far better carrying capacity than the OEM 4/1 springs. Truck sits level loaded with my Lance 820 now and at same height it used to sit empty. The ride is a tad stiff empty though.