mis-fire

Hello all. I have a 1996 Tahoe 4x4. Having 'random misfire' codes. Replaced everything in ignition system (from the top down to the crank pos. sensor) except cam positioning sensor. Tahoe runs good when it runs good. When its bad its bad. Any help would be appreciated. Running out of ideas. BTW...

I just bought a new 2009 Chevrolet Tahoe LTZ 5.3L 2WD 6-speed auto. I've put a little over 500 miles on it. On Monday of this week I went to start the vehicle and it turned over, but the entire vehicle started shaking side to side and the tact was jumping all over the place as well as the oil...