Bet they didn't cut the counterbores when they did your head gaskets. Acerts are known for sunken liners and Cat won't admit they have a problem with liner protrusion. A low liner will cause the block to fret under the liner flange this causes the liner to sink into the block deck surface. Once the liner drops more than .005" compared to the liner next to it, the head gasket is gone! If they're low from the factory they shift and fret the block then they drop even lower. Any time you have one apart they need to measure them and they all need to be at .006". Cat says anything between .001" to .006" which is total BS.Haha well it happen. When we did the rebuild we had the head decked an had to put a spacer plate between the head an block an went with a stage 2 pdi tune no problems yet knock on wood..