My ext cab is hitting 15.4 @ 87mph with just 2.5" pipes after the header to a single in/out magnaflow with a turndown after that, and a k-n cone with the stock intake tube. I can usually take any singlecab that stock, I dont have a posi, and im still with the stock 3.42s and tires so i dont have an advantage. Its weird cuz i hear of trucks that have all this stuff and they are just hitting like low 15s, but i recently found out the reason, its all about location