You hit the nail on the head. It is hard to say without being there and seeing it.
It could be the pinion is still loose causing it to oscillate on decell or the pattern is wrong.
Did you check the pattern with the pression blue? (yellow in most cases)
If not the gears mesh is very important, I would first check to see if you have any side to side movement in the pinion, then pull it and inspect it for damage.
Are you using a solid pinion spacer with shims or a crush sleeve? A solid spacer is best the crush sleeve can only be used once and could loosen up. They also take extreme force to crush some times.
If this is your first gear setup, you should find someone close to you that has done a few to look it over with you.
If it isn't done right it won't las long.
Good luck,
Mark
