I am looking to add power in the long term future of my 2009 3.5 TL 5AT, and I have found the transmission to be a weak spot when gaining power. Are there aftermarket transmissions or torque converters? Or would I have to rebuild with more robust parts?

 

There are shift kits to help improve the valve body on the 5spd trans. Also you can go with upgraded clutches on the inside of the trans. Dr. Evil transmissions used to be the go to source for upgraded tran/torque converters.

The killer for the auto trans is heat; 3G TL-S guys (same trans) are near 500 HP and simply need to let the trans cool between drag/race runs. Some have added a tran fluid cooler and extra fluid capacity to help keep the temps down.

 

How much HP are you planning to run?

If your 5AT trans is anything like the 3G, you can install an aftermarket trans cooler and it will completely get rid of any cooling issues our Autos have. Level10.com sells 500-1000whp trans cluch pack kits and torque converters. Give them a call if your serious.

You will be fine with a trans cooler for now.