I just came across an article on this today: How to Pass Your Next Taxi Audition
While it is about Beijing, some if it does apply here. Getting a taxi out in the north east of the city where I work is a nightmare around rush hour.
It seems Chengdu has slowly increased the number of taxis though and allowing non-Chengduren to drive them. This resulted in me having to tell a driver from Suining where to turn/drive for one memorable journey.