even peterbilt and kenworth had plywood floors way on up to at lest 87 for the petes when the 359s were fazed out for the 379s, kenworth used plywood up to 82 when thay fazed out the W900A's for the new W900B's... in the 70s thay all rode like a buck board wagon even the early air rides, late 80s mid 90s air ride got alot better but still harsh till air ride cabs took over solid mounts early 90s... im no fan of air ride cab, wanta feel what the frame dose but im old skool, grew up in them in the 70s with dad an g'pa, 5 great uncles, 30 some odd cusions, all of us just trashy *** truck driivaa's