The manual on my 08 calls for every second oil change interval (15,000miles) to change the axle oil, front and back. I'm just doing my first change on it now, have about 14,000mi, putting in Royal purple synthetic. Anyways, since Dodge calls for the use of synthetic oil only, it is pretty expensive up here, about $120 for enough oil for front and rear. Any thoughts on if I can extend the drain intervals with the Royal purple or if I should stay on schedule. I was thinking of sampling the front and rear diffs at the next change interval and see what the oils come back as. At $20 a sample it might be cheaper than new $120 every 8 months if I can double the intervals. Wish there was some sort of filter kit for these diffs.