Check the adjustment on your clutch.
There should be a little freeplay at the throwout lever (the transmission end of the clutch cable) when you check it. No freeplay means you're basically driving around the clutch pedal partly depressed. (hence slippage)

I don't have any info on mini-me swaps. (but, I think ODB-2 requires an oxygen sensor after the cat in addition to the one at the manifold)