I bought a 2019 Tahoe with 37,000 miles from a car rental company. During a 1300 trip, the suspension went from just fine to rough as a log truck. Like all four shocks had been replaced with a solid bar.
Long story short, I took it to a dealer, which I seldom do. They diagnosed only the left rear shock was bad. They replaced it and all the others started working right. The reason I'm posting this is nothing I found on the internet mentioned this solution for the problem I had. Now if somebody else has this problem, hopefully they will find this post.
I was ready to remove all the magnaride shocks and struts, then install an after market kit doing away with it all. For now at least, I'm glad I didn't. If another one goes bad next month, I may feel differently.
I wish I knew how the dealer tech diagnosed the one shock bad. The vehicle was stiff on all four corners.