Last week I suddenly got a vibration while on the highway and at first it felt like the motor lost a cylinder and I was only running on 5. I changed lanes and everything was fine for about 30 minutes of highway driving. Then as I got off the highway it started to shake and I could feel the shake/pulsation while braking. I tried braking again and it was fine, no pulsing or shaking. Then as I pulled away from a light it started to shake/pulsate violently and I had to pull off the road. I made it home and I thought it might be the master cylinder acting up. So I put in a rebuilt master and sure enough I got the vibration again. 95% of the time it's fine and brakes good and straight so I don't think it's brake or rotor related now. But while it started to shake today I pushed in the clutch and no difference. I shifted into neutral and coasted and it was still shaking. So I'm thinking either suspension or driveline. The shocks look good and feel pretty stiff still. The driveshaft looked fine and felt like it was in place good and firm but I didn't get a chance to jack it up and rotate it. It will just suddenly decide it wants to vibrate and shake and I have no idea what the real problem is. Any thoughts?