I run Royal Purple in my trucks as well as big engines I have 28000 mile on my last oil change I change the filter every 3000 miles and take a oil sample and send in for analysis the oil sample kit comes from Stewart and Stevenson like 12 dollars and that includes the analysis I have 148000 miles on this truck and am on my third oil change after brake in of 3000 miles I have 3516 Caterpillars with 10000+ hours on a single oil change using the same method with the addition of a Spinner 2 oil filter. The bang for your buck with a good synthetic comes from the proper analysis. This also can predict engine failures and dictate proper preventative maintaince as well. Best luckCurious on the use of synthetic oil. Bought an 07 2500 and would like to know if it would be worth the extra money to use synthetic when I get the next oil change. This is the first diesel that I have owned.