That's probably not gonna make the ride softer like OP wants though. They just want plush. Pretty much all 5100s do is make the ride especially rear end more controlled.If ride quality is your main concern for like $1k you could upgrade the suspension to Bilstein 5100s or something. Cheaper than throwing a couple grand in the trash on a trade.
I just think the problem here was still a problem of perspective, from being too accustomed to worn-in GM suspension. Highly doubt the factory's choice of a different brand SL highway tire is gonna be responsible