We frequently use the GM M70 transmission known as the 4L70E.  This is a RWD only transmission and is readily available from Chevrolet Performance.  This transmission comes with a factory torque rating of 495 ft.-lb.s, which is slightly betting the a stock 4L80E rated at 440 ft.-lbs.  This transmission also comes in lighter than the 4l80/85E by 20-22lbs.  What I would like to discuss is the differences you may run into when wiring or choosing a controller for the 4L70E.  We have now ordered 4 of these transmissions, 2 came with a 13-pin connector and 2 with a 15-pin connector.  From what we have found, in 2014 GM changed the 4L70E back to the older, and common with the 4L60/65E, 13-pin connector.  Before you order a controller or choose a wiring harness, make sure you have the transmission and count the pins.  

For instance, from FAST the EZ-TCU controller:
13 and 15-pin connector – EZ-TCU™ GM OVERDRIVE TRANSMISSION CONTROLLER; 4L60E, 4L65E, 4L80E & 4L85E; UP TO ’09  Part #302820
17-pin connector – EZ-TCU™ GM OVERDRIVE TRANSMISSION CONTROLLER; 2009+ 4L70E & 4L65E  Part # 30299-KIT