I bought the wife a 1999 Jeep Cherokee with the 4.0 six cylinder engine,it has 30K and is in excellent condition.This is her 2nd Jeep.The first one went over 150K using 10w30 dino oil(it was in a bad wreck and was totalled).This one I'd like to use Super tech synthetic along with a Super Tech filter.Normally I change dino oil at 3mo/3000 mi interval,but would like to extend the change interval when using the synthetic.Comments/suggestions??