I've noticed the biggest problem when I'm chasing someone that has cloaked is that it's a lot more difficult to even hit them before they're invisible for the first time. I just used Cloak for the first time and it was a dramatic improvement as far as my score went. I don't think it's random coincidence. So here are my suggestions on how to make it less overpowered and a little more fair. Also, I used cloak + Vot Bolter for my cloak test rather than shotgun, and still found it grossly overpowered.
1. After a player shoots while in cloak make it so they are fully visible for a slightly longer amount of time.
2. While they are visible allow the cross-hairs to turn red and bring up the player name like every other visible player. (AKA: Player shoots, until invisible cross-hairs change colors and name appears)