I would highly recomend that you pour a 1/2 bottle of sea foam into the oil, and the other 1/2 into your gas tank. This will help to clean out the rings. Also, you will need to pull the EGR off and clean it too.
Only cleaning 1 of three isn't going to help slow down the oil useage.
my 2 cents.
-Ryan
http://www.geocities.com/endre_rl/isuzufaq.htm#faq4
As for Oil useage, I was reading my CD manual last night, and it stated the following reasons for increased oil consumption: 1. Dirty EGR (system) 2. Dirty PCV 3. Carbon up piston rings 4. Long highway trip 5. Towing