Lexus RX 350 94k miles

What did you find out?

Has this vehicle had a tuneup and throttle body IAC cleaned out?

I recently had some work done as far as tires changed and also oil change and brake job shortly thereafter the engine light, Vsc and skid light came on. I was told that it might be a gas cap issue when I called Lexus. I tightened the gas cap on several occasions and it still did not solve the problem. Recently, while driving on the expressway, my car began to lose acceleration even with my foot on the gas. Then suddenly it would get a burst of energy and speed up and then the acceleration would decrease again. I had it towed to Lexus who initially told me only three of the six cylinders was operating and it needed spark plugs, a water pump and a belt which I had done. They then came back and told me that the light was still on and recommended a new O2 sensor which yet again I had done. $2,200 in, they called me and told me that my vehicle was fixed. However, before I could get off the lot the lights came back on. They then stated that the fuel injectors were clogged and that they were going to clean them. Called me back and said that did not solve the problem and that the fuel injector in cylinder one is clogged and now they recommend a new engine for $6,500. I am at my wit's end with this situation because they have yet to solve the problem and I'm not really feeling confident about their diagnosis. They keep telling me that the codes are only coming up one code at a time. Any help or suggestions would be greatly appreciate it. It is a 2008 RX 350 with 151,000 miles. Any help or advice would be appreciated