Bobber
I'm a PT student (and also have crps) if you can wait a couple of days I can send you some generic information about TENS with specific programs and also some info my PT has put together regarding patients who have crps and how they should use TENS. My laptop which has all the data on it is currently being fixed lol.
I find that a lot of PTs prescribe TENS without really remembering or knowing the principles behind it, one of my tutors has just had a big paper published on its effectiveness but not specifically to do with crps patients..

Anyhow let me know and I'll pm you some useful information to help you test it out in ways that will test it most effectively for you and fingers crossed actually provide you with some relief!