They use both the 8.1 and 6.0 I'm positive on that well at least in Ohio with ODOT and all the other local government places none are diesel too. And you are correct they used the 6.5 a lot, you can still buy the old ones from the government with the 6.5 and most are in great shape.if im not mistaken gov agencies use suburbans with either the 8.1 or the 6.0 they would have to have the diesel engine put in them because chevy doesnt sell suburbans with the duramax, they used to have suburbans with the 6.5l diesel though, correct me if im wrong![]()