Car shakes

What is your question?

We'll, I don't know how to describe the shake. All I know is that the car shakes to the point that it can be felt on the seats. I don't know where this comes from. Regarding my visit to the dealer, the dealer inspected the car and said: There was carbon on some stuff and they cleaned it as well as Cleaned the fuel injectors. They also said to have put what they called "additives" to the gas tank and Said to run the car until the gas sign came on. They said I That this could fix the issue and that if not they had to peen up the engine. I picked up the car and drove away from the dealer. About seven miles later the engine sign came on and the shaking was back. I went back to the dealer and they said I had two options: 1- run the car until all the gas wears out Or 2500 to open the engine. When I asked what the problem was, the dealer had no concrete answer. I must say that the two days before I decided to take the car to the dealer, I had the car at pep boys and they did this: changed the mass airflow sensor. Cleaned the fuel injectors Changed all spark plugs. When I went back to pep boys they gave me back all the money I paid. So since the dealer asked for so much money I decided to Take the car to a mechanic who had repaired the vehicle when it was involved in a hit and run. In the midst of this I read about onstar diagnosing a miss fire on a hummer with similar issues. I called onstar and they said it was a miss fire P0300 code I gave that information and even this very website as well as some others who also say of similar issues. That mechanic did this: Replaced fuel injectors, Replaced crank shaft sensor, Replaced all coils. This was just one week ago Friday June 20, 2014. The car was so smooth that I couldn't tell when it was turned on. On Friday June 27, 2014 I felt a minor shake every time I came to a stop. I called the mechanic who said that maybe someone could be messing with the car by putting water into the gas tank and to buy a gas lock. I bought the gas lock and some stuff that evaporates water. Yesterday the shaking was full fledge again. I must say that this shaking occurs when the weather is really hot. Friday and yesterday it was very hot in NYC. I noticed that the needle for heat in the car on Friday was just in the middle and Saturday it was a little bit past the middle. In any case I have to take the car back tomorrow. The mechanic says that it can't be the cylinders because The exhaust would throw some white smoke??? He also said that it may be some gas filters? I simply told him that I want to rule out the cylinders by inspecting them with a computer used for it. He agreed. I'm tired if guessing. I'm already 2,000 dollars deep into it and nothing has cured the problem. I'm stuck in a catch 22. I love the car but I'm not going to spend half of what I still owe to the bank on the vehicle. I rather trade it. But I never wanted to get into another financed vehicle. Not what to do with this crappy issue. No one has been able to pinpoint what the problem is. If anyone has any suggestions please send me an email at: gp1182@gmail.com I need some serious advice here. Thank you for your help. Greg Perez