Sounds like a head gasket. Prior to boosting it, what were the supporting mods, i.e. arp studs, and a mls or cometic or a copper head gasket? That is just the bogging issue. takes a second for the water to get burned. now I know your thinking, but I dont have white smoke, could be just a hair drip inside. ka24's have that aluminum head that is known for pushing gaskets, and warping when hot.
For your vaccum and afr, Its been a minute since I messed with a ka24 but what about the egr diaghram? Had a 22rte give me shit for a day on a weak vaccum line.
Then again as you said your going to check your TPS, the most common sympton of a TPS Going out is stumbling during acceleration.