I am pretty sure down time would be about the same. It might cost you less to put the truck in the shop and have them run the rack, then maybe change the cam. You might just need a lower end rebuild. I would check with a few different shops in your area, their price might differ and so might your down time. I know the DD series 50 engines are a very good class 7 engine, everyone I talk to that have them in their truck loves them. I mentioned TSI because I have done business with them and they are an honest shop.