It sounds like a cat converter , power ok and high gas consumption, I drilled a hole just before the bend before the cat from the engine , the size of the straw from a Sea foam spray can for cleaning fuel injectors Corbin and throttle bodies I sprayed it in and ran the trailblazer and it cleaned it up and senses, I saved money and getting a new cat. I put a ribbit In the hole and a clip around it. Never had a problem ever again. Great power and gas for the mile. Ps it will smoke for a few mins.I got a trailblazer for my Son paid 4K total it had low mileage and looked fairly clean inside. There were a few things I knew about like New shocks, rear trailing arms i had to fix then found it needed valve cover gaskets because there was oil on the spark plug boots, then new front hubs and steering sensors because of abs lights and codes, and a few odds and ends.I fixed all this myself and thought it was good to go I was wrong, he kept going to the Gas station alot. I accused him of idling and listening to the radio goofing with friends you know the normal teen stuff. So I filled it up drove it for a while and Poof I checked the MPG and its under 10 mpg over 3 tanks now no matter who is driving. I purchased a Blue driver tool and pulled 2 logs from a trip to home depot. There are no codes in the system and Im at a loss where to go from here.? I thought Fan but the fan looks like it is functioning properly, Then O2 sensors but im not sure they are bad. Thought termostat but the numbers look right there also. I have attached the logs as a text file but they are exports from bluedriver and csv files. Anyone have any insight. Its an 07 TB 4.2 i6 4wd LS 105K miles. It idles fine no stalling the power seams ok but its hard to compare it to my V8 truck. He loves the truck but sub 10 MPG is not acceptable.