I need to replace the rear shocks on my 15 Yukon XL Denali. I'm looking at the Arnott 3066 and 3429. The only difference I can see is the 3066 is mono-tube and the 3429 is twin-tube. Has anyone used the 3429? What are the factory rear shocks, twin or mono? Or does the magneride even fall within those two categories?