2003 Chevy Truck DIY Project gone wrong

My truck was shaking and idling rough, so I got a complete tune-up at a shop(wires, distributor cap, spark plugs, etc.) The problem was still there so I let the shop do a diagnostic and they said it was the 2 02 sensors. I replaced them then the shop said it was the fuel pressure regulator. By this time I tried to save money and replace it myself. I bought the alldata diy and replaced it simply. Then the car wouldn't start, sounded like something was keeping it from turning over. So I replaced the battery. Still wouldn't turn on (could hand crank it, but the stuck sound was there). After waiting a week (to get more money in the bank), I came home to find the car leaking gas and maybe mixed with oil. I hadn't even touched the car, so unsure why it suddenly leaks. Trying to narrow down issues before going back to dealership. Any ideas?