Good story and great detective work. Attention to detail solves a lot of problems. Unfortunately, shops often recommend a new ECM when they have trouble diagnosing a problem. It seems that your problem was the quality of the Standard Motor Products RCM. Not uncommon as the quality of aftermarket parts continues to decline. About 5 years ago I replaced the RCM in my 2004 (for insurance) with an OEM MB unit from a dealer in Florida. Surprised at how inexpensive it was (maybe not anymore). Has worked well.