There can be several reasons for a delayed shift. But, please understand that the shift solenoids are on/off (they either work or not) and are controlled by the PCM based on line pressure. The line pressure is controlled by the pressure control solenoid or PCS, which is often to blame for 'soft' shifts or 'late' shifts as well as slipping and delayed engagement of drive or reverse. Do you have any other symptoms? When the shift is delayed as you describe, do shifts become more harsh? When the computer detects a 'late' shift, it will cancel 'adaptive shifts' and will tell the PCS to deliver 'full line pressure' whch will create harsh shifts and can wear internal seals quickly.
Although I have not done this repair on my Montana yet, I have done it to both my Impalas which have the same transmission and solenoids. Lowering the drivers side of the engine is necessary to remove the transmission side cover. This also requires the loosening of the engine cradle mounts and removal of the drivers side wheel and possibly the strut (for ease of access). I have also installed a Transgo shift kit to both quicken the 1-2 shift and to reduce wear of the #2 clutch pack.
Hope this helps,
Ian
