1994 Infiniti Q45 steering wheel and car shake

My car starts to shake at about 65mph and higher. Tires have been balanced and rebalanced several times to no avail. It happened with old tires and wheels and now with brand new tries and wheels. The bearings have never been done but the Infiniti dealer says they are fine and don't need it. Says everything is tight down there. The shaking seems to be worse when the car has been sitting for a few days and seems to shake slightly less when car is good and warm. The car runs fantastic other than the shaking problem. It also at times feels as though the entire car is shaking along with the steering. I've also been to specialty tire shops and still shakingl. Brakes are fine and all shocks replaced about 3 years ago. They have about 20,000 miles on them. Drivetrain replaced about a year ago. It is extremely frustrating, for this has been going on for about 2 years. Please help!