2015 Silverado vibration

[fstgmp]

My 2015 Silverado has had excessive vibration at speeds above 70MPH on smooth roads since the day I drove it home from the dealership. I have 47,000 miles on it and the front tires are coming apart in pieces while the back tires still have considerable tread left and no damage. I've had numerous tire rotations, tire re-balancing and four wheel alignments done from five different garages, (including two GM dealers), and nothing has helped. I've just paid $900.00 for four new tires and a complete re-alignment, and on the way home, I got out on the highway and at 70MPH my passenger seat and armrest started shaking from the vibrations.I don't want to ruin a new set of tires. Can someone please help? (Make that six garages).

[silveradosid]

have the driveshaft checked, it was the cause of my vibration