You must have a VSS signal for the PCM to work correctly, if you use a non-computer transmission 350, 400 2004R etc you will need to find a method to generate the VSS signal. Here is a link for solutions to the VSS problem.
http://www.jagsthatrun.com/Pages/Spe...eedometer.html
If you use a computer controlled transmission the PCM/TCM you are able to use will determine which transmissions will work. In my case I had to use a 4L70E because of the need for a input speed sensor that the TCM required. My combination is a 2008 LS3, 4L70E and factory Corvette PCM/TCM reflashed to removed the unnecessary functions.