One cool thing about the GPS + Infiltrator that everyone who's already posted probably knows, but may be helpful to newer players:
Releasing an already charged shot will not break Tactical Cloak. Thus you can get Tactical Cloak's bonus damage on two shots, one that you had charged up before you cloaked and you release while cloaked, and a second quick-shot (not charged up) also while cloaked, which will break cloak. Basically it's the act of pulling, not releasing, the trigger that breaks cloak.
When I had a thin manifest, I'd use the GPS a lot on the vanilla Human Infiltrator because it was the best weapon/character combo I had at that time. (No GI yet, for example.) The combination of charged shot w/ cloak bonus + noncharged shot w/ cloak bonus will kill a lot of enemies in one... er, well, two... shots.