Q: Transmission replaced, but still slipping - 2009 Kia Borrego

The transmission in my SUV started slipping. It would stay at 40 mph with my foot off the gas pedal and slipped in 3rd and 4th gears. When I took it to the repair shop, I was told that my vehicle needed the transmission replaced. I had to pick it up until the new transmission was shipped to them. The day after that, the check engine light came on and I called the dealer. He told me that it would be okay to drive my SUV with it on and to wait to bring it in when they received the new transmission. My SUV’s transmission was replaced with a remanufactured one and they had never told me that it was not a new one until I picked it up after they had done the work and I read it on the service ticket. It was only 200 miles later that the replacement transmission started slipping, like the previous one. The jerking was very hard between Park and Reverse. Then the service engine light also came on. When I called the dealer, they were too busy and I had to wait several days before getting an appointment. When the appointment day arrived, I went to drive there and my SUV would not go faster than 20 mph. I made it around the block and decided to take it back home and then it would only go 15 mph. I had to pull out onto a very busy street where the speed limit is 45 mph and I could not get the car to move! I had to have the vehicle towed to the dealership. On top of this problem, my SUV has had gas tank problems. I had the tank replaced, but now the code says it is at lethal levels. I’ve been to the dealer four times to get the airbag light off, the seatbacks are falling off, the paint is chipping, and the list goes on. What are your professional suggestions that will help my car’s problems?