Just responded to your post over there. Best of luck in troubleshooting it.

 

Just replaced my fuel pressure regulator, and this problem was improved quite a bit. RPMs still drop a little after starting the car, but not nearly as much. Overall, the engine is more responsive to throttle changes. It is a very noticeable improvement.

I'm also going to try an injection cleaner before my next oil change, as that has seemed to help others here on NAM without similar issues.

 

I'm having a similar issue on my 2005 MCS. lately I've noticed rough starts and much lower gas mileage, only 65,000 miles.