Engine Exhaust System problems of the 2007 Toyota Sequoia

Exhaust fumes in interior when accelerating.

I have 2007 Toyota seguoia, in the last 2 months I, as well as my friends, have noticed a very strong odor of exaust fumes accumulating in the cabin of my SUV when: -accelerating to pass -decelerating from passing -stronger when a/c on and in "recirculate mode" -also when just regular a/c on the fumes have caused my friends to become ill with nausea, headaches, and sleepiness. The fumes have caused me to become very sleepy when travelilng, and my friends say my thinking is off in last couple of months. I took to local Toyota dealership, and they told me that they did not notice it? then told me they would not investigate it further because no notice was out? my SUV has 24k miles on it, I have owned it for one year. This is a severe passenger safety issue, it is going to cause someone to fall asleep at the wheel, and kill someone else or self. It is also danger to passengers in car in multiple avenues. I think this needs to be investigated ASAP! thanks!.