What front der are you using. what shimano specs fo that shifet on a triple is r443a. The one thing about the derailuer is that you want the outer cage plate of the der to be parrallel to the chainrings (and just a mm or 2 above the outer chainring) instead of the inner cage plate
here is the link to the teck docs for the shifter. towards the bottom there is a trouble shootong chart that describes your problem