I have a 97 Tahoe with a 5.7 engine. When driving around town, it runs like it has water in the gas. I have tried several different tank additives (fuel injector cleaners, gas treatments) and different brands of gas, different octanes. Nothing helps. Can someone point me in the right direction please? Also, when I apply the brakes, the pedal is soft and goes a long way down and if I press very hard, you can hear and feel a thump, thump, thump. The vehicle stops okay and the ABS is working but the pedal is very soft and the thumping is very annoying. And yes, I have checked the brake fluid. Please help!!!