weird vibration

[miked.]

maybe someone has gone through this. after about 45 minutes of driving, mostly stop and go i get a vibration. its like flat spots on the tires. only happens after i drive more than 30 or 40 minutes. it shakes the whole truck. could it be the tc.? i do need rotors on the front. i don't know if that would cause it or not. 2001 f350 cc lariat 4x4. thanks for any input.