oil question. front suspension question

[scott]

Here's a additional question. I had oil changed. Went almost 20,000 mile. After the initial start up. Recheck in oil. It already is turning black. I assume it means my cummins is dirty. I am gonna change oil again at 15,000. Obviously bypass filter would help. Am I correct that there's alot of dirt etc. Everytime I change oil it does it. Shops just say it's normal.