I have an 87 K5 Blazer that I have swapped in a 5.3. The motor is stock with just a free flowing exhaust going to a dynomax muffler and a 4" cold air intake. I had the truck unlocked and set with a base "performance tune" for premium fuel. This was all before I got HP tuners and started tuning. I have touched up all the fueling that was majorly off. The truck still gets terrible MPG compared to other swaps I have read about. I know my trans pump is weak and is probably causing excessive load on the motor resulting in mpg loss. The main reason I am posing and asking for help is I have light knock in a couple cells. I have tried the tune with 87 oct. after seeing the timing looks nearly identical to stock, so I didnt see how this was a premium only tune. After noticing I did in fact have some knock I tried it again with 91 oct. and it still has knock at the 2000 - 3200 rpm range across 55-85 map kpa cells. The reason I don't just pull timing is my 01 1500HD with 6.0 running a totally stock spark map with just some fueling fixed shows this same general area having knock. Do these motors just have a knock problem in those cells? Please check my tune file and my data log. If you guys notice anything out of ordinary or that I could tune better I would really appreciate the input. I have it in VE tune mode right now and I have the VE table pretty much dialed in to all 1's and 0's at this point. I just realized I cant upload my tune files on here because they are not a supported format... I can email HPT log and tune to anyone willing to help me out!