Just to tag onto the manually shifting side. I had never driven a diesel vehicle until buying our Dutch Star 3 1/2 years ago. The first two years I let the transmission do it's thing. The result was higher engine temps and slower speeds up most grades. I learned from the guys on this forum and started downshifting just before the grade and the "need" to do so. My coach runs so much better!! I have read that the Allison won't hurt itself, or the Cummins and I believe that to be so. I am the old guy in the old coach that is hard to pass!
Owner of a 2003 Dutch Star, model 4007
2003 Chevy Tahoe