Allison Man: I have an allison 1000 on a 2004 Chevy 2500HD Duramax with 180,000 miles. I had the dealership flush the system in May 13. I change the filter every oil change and just change the filter 5 days ago. All of a sudden, my reverse has a delay and then clunks into reverse, and my lower gears have an extremely elevated RPM before they clunk into gear too. Changed the filter in case I had a bad filter. It didn't help. What do you think?