Loss of power

Second week with truck. Engine light came on hours after purchase. Bought it as is condition. Took to Bel Tire was told to take to Ford the computer needed to be reprogrammed and they could not do it. Took to Ford dealership was told that core 7 (I may be saying the wrong part) was bad I payed $400.00. Which included $119.00 to check the service engine light. Drove off okay until I go to my trunk after shopping and see the engine cover. Called and was told it was the wrong cover. Two days later the light came back on. Took back in because I was told I had a warranty. Ford says the warranty was for the core 7 change. They double checked their work. No issues. I was then told that the vehicles codes were reset improperly and a code of p1200 will keep causing the service engine light to come on but if I wanted them to look deeper it would cost another $119.00. And to let them know if there is a loss of power. Friday I jump started my car. He checks my oil no oil on dip stick. I called Ford in which I am just now being told it may be the wrong dipstick. Yesterday driving the vehicle started to drive slow (i guess the loss of power mentioned) rpm's jump to 3, 00 to 4,000 truck mph's slowly rise. I do not want to take back to Ford. Feeling hopeless.