Engine stalls on stoplights with new o/r h-pipe

[daz95gt]

I just bolted on a flowtech O/R H-pipe and the car stalls almost every time i let the gas off (& press clutch) and let it idle. It then tries @ about 300-400rpm to add revs but it's usually already too late for that.
All (2) oxygen sensors are right in place and there is also a hole in H-pipe for air tube which originally was for cats which is in place. I get no check engine lights.

Should i just reset the computer by disconnecting the battery or where does this problem come from? The car is bone stock 95 GT except 2.5" ultra-flo's & k&n.