Pop Then Slug?

Check your timing? Something similar kinda happened to me, my distributor hold down clamp came loose and my dizzy moved a little bit and the car had no power at all, 5min fix though.

I see you have a catted X pipe, which brings me to a situation I had at work last week. A honda accord came in with the same problem, it kind of make a pop sound in the exaust, loose power, then another pop sound and power came back quickly. Found out that it was a converter that had come apart inside and the chunks would get in the right position and block the exaust. Replaced the cat and the exaust system, problem solved. The car had a lot more go after the new exaust.

Check to see if your cats are rattling or if there is any in the cat-back.