The Cummins 8.3 has been around for a long time and it's the best engine for mid size DPs. The ISL 400/425 is nothing but a stroked (8.8L) ISC and it has proven to be a good engine too. 50K miles is nothing as I have a FL 70 with the 8.3 and 350K miles that runs great and gets good fuel mileage.