Might be worth removing the driver's side hard pipe from the throttle body and look for an obstruction. I accidently left two blue shop towels in the lower pipes while I had my upper pipes off of my previous Z. I forgot to remove them prior to reinstalling the upper pipes. I had a high idle which about wreaked havoc on the Auto tranny and they nearly made it past the throttle plates into the intake plenum. I was bewildered until I finally had to take off the pipes and look. Sounds like you have a much more subtle problem but with all the work you performed with other folks involved, might be worth it to you to at least look. Good luck and hopefully you find the solution.
