The ISM, formerly the M-11 is a great engine. I prefer the M-11 because the mechanical version never gave us problems, but the basic engine is very good. We have spec'ed some trucks in the past with the 300HP M-11 and pulled 80,000 pounds with no problem.
We kept them about 500,000 miles then sold them. One still belongs to a hay farmer in Kansas and he has put another 200,000 miles on it and loves it.