Just finished putting a LS2 from a TBSS in my 09 tahoe and also installed speed engineering headers and y pipe at the same time. I was real leary about a LS2 since I have been using nothing but LS3's for a few years but couldnt pass up the deal on the LS2 since it only had hundred miles on it. I have put 300 miles on it since being done and wow it drives so much better with the ls2 over the 5.3. So far the mileage is averaging out a little better than the 5.3 was. Its a little louder than I expected with the headers and the stock muffler but its still quite cruising on the highway for the most part unless you hit a hill. Since the motor was basically brand new I wanted to put a few miles on it before throwing it on the dyno so its just street tuned now. I plan on getting to the dyno next week to see what the gains are over the 5.3.