Engine Light, Vsc off, Skid light

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 and or
invites will be greatly appreciated!