trans problems

my trans is driving me insane...some days it seems to shift very well. But lately it has been slipping on takeoff in the higher gears (D,3,2) If I pull the shifter down to 1st gear it will not slip at all, if i punch the gas it will just squeal the tires in 1st. If i hit the gas in drive it slips a bit and will grab and go once i hit 15mph...less noticable in 3rd, even less noticable in 2nd, non existant in 1st. The trans also has a bit of a soft shift (studder shift) if I drive it harder in drive...but again shifting is BANG ON if I were to shift it manually. Local stealership mechanic said its likely the torque converter not locking up in drive...anyone else had this issue? I added a tube of lubegard shudder fixx and that got rid of the shuddering, but not the slipping.

This should be scanned by a trans tech with a trans function scanner and look at gear ratio errors, solenoid functions and trans codes, I do not believe the TCC is the issue with your description it just sounds like either it starts in default 3rd at times or is just slipping. In the future it may help to post the year and mileage, but from a symptoms standpoint, in this case not an issue.