3,000 miles of towing heavy and all of the above on rotella t6 ck4. Switched to Schaeffer's 9000 5w40 cj4. The ck4 actually did well, probably wouldn't need to switch to Schaeffer's, but going to run it to 5,000 miles now. Oil was in the sump for 2 years. Call me crazy, but I do think the engine...