Help Help Help!!!!!!

Recently my Subaru went into a garage and had 2 Alpine V12 amps fitted with various other speakers.
But since i got it back i have been having trouble making the car boost correctly!

It will drive around brilliant for ages then all of a sudden when in 3rd gear about 5 to 6k revs it pulls against the boost as if a cylinder is missfiring!

Atleast thats what it sounds and feels like!

The car however did not have any problems before the work was done and the mileage was recorded before it went in to make sure no hooliganism took place!

Or could this be the result of a dirty sensor or something?
Or power issues due to the extra load on the car from the amps??
Any information would be greatfully accepted!

Cheers!!!!

 

dissconect amp cable from batt, and then see if it does it, if so then its nothing to do with the extra surge the amps need!