sluggish in 1st gear sounds abit weird, if i pop mine into 1st and floor the throttle, i get a little traction control error logo appearing and goes away , it pulls hard and snaps into 2nd gear less than 3-5seconds.
Are you pulling away in "D" mode or shifting it into tiptronic mode and selecting 1st?
if you in "D" I believe that this is 2nd gear. and not really 1st. your car has enough torque to pull away in 2nd. i would guess that all e90 autobox's 1st gear are relatively still brand new and it HARDLY uses 1st gear to pull away.