Can We Talk About Wheel Bearings and Grease?

[C10_ustacould]

I recently replaced my front brake rotors and wheel bearings in an effort to calm vibration. Combined with re-balancing my wheels and tires my vibration was reduced to nearly zero. After 350 miles, a slight vibration has returned. Not nearly what it was, but it is there at about 60-62 mph. I checked the front wheels and found that there is some play in both front wheel bearing; I wouldn't call it slop but more like endplay. I used Timken bearings and the part store brand grease. I did not remove the existing bearing races, but simply installed the Timken bearings and set the Timken races aside. At this point my suspicions/questions are: 1) Should I have swapped the bearing races, is it a big deal? 2) Is it possible that the wheel bearing grease is insufficient and if so is there grease that stands above the others? Let me know what you know... Thanks in advance!