If the Avenger uses the Chrysler 4-speed auto (I'm reasonably sure it does) you can get a shift kit from:
http://www.txchange.com/sk.htm
The SK® 604/606JR would be the one you would need.
Some people have reported that after installing the kit, they clipped (or put a switch on) the "Request for Torque Management" wire that runs from the TransControl Computer to the Engine Computer. The RTM reduces the power from the engine during shift to lesson the wear and provide a smoother shift. With the wire cut, the engine provides full power during the shift and when the kit has been installed and set for very firm shifts, tire chirping occurs on the 1st to 2nd gear shift.