I don't know, I think with Tate's durability issues you are in the perfect situation with the guys you have now.
The running back position is secure and you can use Tate as much as you want or need without worrying about pushing him to hard because you have good starting caliber options behind him.
It would be great to flip one of them out for a starting caliber WR, but I don't see anybody giving up that kind of player for either a 3rd round running back or an undrafted one. If you drop any of them the the PS they will be picked up by somebody. Hopefully one of them can help pick up the slack on special teams.