DIC Issues

I have and 2007.5 duramax and I am having some issues with my DIC for Oil changes. First two went normal about 1% drop for every 100 miles or about 10K per oil change Exactly what I experienced with my first two trucks. Right after my 3rd oil change things went bad. after about 600 miles the % would drop about 10 points and then do nothing for about 400 miles and then take a 15 point drop and then another 200-400 miles and another drop only greater. Dealer said Chev told them it was a vacuum leak. THey checked and found a vacuum leak and the problem went away for about 1K miles(normal 1% drop). Problem returned after that and they told me since I changed my own oil the couldn't prove anything and no leaks this time. I had them change the oil (about 1200 miles on it). And started the clock over. WOrked normal until about 300 miles and then dropped to 90% stayed there for 400 miles and then dropped 14% in just under 50 miles. NOw they are telling me that they can't find anywhere that it says I should get 10K between oil changes. ANyone seen this in there trucks? NO change in the driving conditions or they way I drive this truck no heavy towing About 50% 3 mile trips and 50% trips over 25 miles. Same driving different results. I suspect by reading some the blogs that maybe the have changed the programming for the oil monitor the last time I was in. Can they do that. At the rate this thing drops it looks like I will be lucky to get 2K between oil changes as everytime it drops it drops with larger percentages.

Any INfo Greatly appreciated

Norm