the ATTS tranny experiences a little more parasitic loss as it transfers torque to the wheels.
157 whp isn't bad. with the right bolt ons, a VAFC, and some tuning that number could be a lot closer to 180-190. Also, look into lightweight 15's or 16's and undersize the tires by a little bit and it'll feel much quicker.
the lude was never meant to be a straight line killer, esp the SH. but find the right combination of curves and you'll see it shine. take it to buttonwillow or the streets of willow and you'll enjoy it much more than you would gunning it at a light.