Would I have any problems running my stage 2 map with a us sti top mount?? Anyone running this

No you will not have any problems at all my buddy did it and it seems to hit target boost quicker.

you can run any TMIC you want on the stage 2 map. however to get the full benefit you need to have it tuned for.

How much of a gain would it be?

you can crank out more lbs. of boost (guessing 1-2??)

I just installed an STI TMIC on my 05 WRX and it works nice with the Stage 2 93oct. Cobb OTS map.

without tuning you might see slightly more boost... maybe 10HP, maybe nothing. with a tune you can probbaly crank out 20hp depending on the tune and size of the TMIC.