I'm also new to diesels and to the forum. I recently bought an "06 GMC LLY and this thing rocks!!! From my readout on the dash it looks like I'm getting around 17 mpg. I have 23 mi one way trip to work, couple trips around town and back home....that might be were I'm getting this. I also want to do some bolt on performance and it looks like an exhaust is the first thing. Is removing the cat illegal? Is it really something I need to do? What type/size tires are you guys running? I'm looking at going with BFG 285/75 16s. Had them on my '96 Z71 and really like them. Any inputs and I look forward to hanging out here.. Peace.:beer