Does anyone know why (& when) Michelin discontinued making the XZA 3+ RV tires ?? I recently purchased a 40' 2003 U320 Tag & all 8 tires are like new 275 / 80R 22.5 XZA 3+ LRH (DOT dates all late 2014). I'm curious if there was / is some type of defect or sub-standard quality issue ?