Hard Shift and Loss of Power

I have a 2005 Pontiac Montana SV6 front wheel drive. it started recently to shifting very hard and sporatically, It also has caused the engine to stall occasionally and have very little power then a hard shift and it is ok again for a little while... Any ideas what is going on and can it be fixed or is it likely the torque converter meaning a full rebuild needed?

Harsh shift is usually caused by full line pressure.....certain transmission codes will cause the PCM to command full line pressure.....some codes don't turn on the CE light, or in some cases it has to fail the drive cycle two times in a row.....

you need to determine where the problem is coming from,,,,,,pulse mod///solenoid pressure rise is dictated by engine computer,,,,,if engine is not peforming,,causing you to step on gas pedal harder,,,,this tells computer to tell pulse mod to raise line pressure to protect trans....you can fault transmission but it is a load device,,it only works as good as the power delivered to it ......crappy power (engine),,,,,poor transmission peformance.....