rbutler's symptoms sound just like I had a few weeks ago. I changed the CPS to no avail then sent my RCM out for repair and that solved my problem. Mine had 13,000 mi. at the time. So from my recent experience I would go RCM. I spent a total of less than $100 for both repairs.
Yes, I just got a MB RCM ( old part number, but works fine ) off eBay for $25, pop'd the cover off to inspect and found it was BRAND NEW ! - no contact burns and the 3 solder joints were solid.
Installed in the car to test and it worked finer than frog hair.
I know, no picture or it didn't happen :