I installed the GM original Jimmy ECM sent to
www.wait4meperformance.com on Thursday. WOW!! I noticed the idle change right way! The updated spider loves the changes. Engine revs past 5000 RPMs on WOT shifts. Tranny shifts are awsome. The 4 door Jimmy jumps out of the first gear. Accelleration is great! Downshift and jumping on to the freeway are no problems at all. No hesistation when I stomp the throttle. I have to feather touch the throttle because it's sensitive. The corrected speedo is nice too. Best $85 spent on the Jimmy!! The tank was 1/4 gone so I can't report on milage improvements. I'll report back later.
If you own a 4 door, get the PCM updated!! 2 doors will like the performance even more. The 4.3 responds very nicely to the changes.