Help. I have 2008 cummins auto 2500. started shifting hard into 4th gear, then lately only shifting out of 1st at high rev and then straight to 4th and not out of 4th until you come to complete stop. Also won't downshift from 4th and run through engine brake-kinda like neutral. changed fluid and don't smell burned. hoping its not major. Don't think it has slipped any before I shut it down. Any ideas? Thanks again.