I have a 350 Vortec in my 00 Blazer. The tune is just about right. I took it to a dyno tuner and he said he didn't really have to change anything, but I still think I should be getting more hp and better mpg. A guy that did almost the same exact swap is getting 25mpg while I get 16-17mpg. The only real difference is that he is running true duals and a stock cam whereas I'm running a single muffler and LT4 Hot Cam. I've noticed my exhaust has a slight gas smell, nothing real strong, but I think it's running slightly rich. Anyone know what I can do?