vibration driving me nutty

i have a 95 suburban 1500 LT. and this vibration problem when at speed,, feels as if i am bottoming out the suspention. feel it in the floor mostly. it when i hit a bump that floats the truck not like if it was a pot hole. so far i have change both R/L hubs R/L CV joints. front rear shocks. tie rod ends inner nd outter,, have have gressed the yoke but did not seem to help this vibration, anyone got ideas