When I drive the car it seems like I have a flat. Only when I step on the gas, when I let go, the ride is smooth again. They checked my tires but all my tires are ok. Also, when I step on the gas it seems like its skipping. They changed my radiator because the light keep saying I needed fluid.
What does this mean?
From what you’re saying I’d be looking at the transmission. Check the fluid. If it’s dark brown or black, or smells bad, get a fluid exchange from a reputable mechanic - not some joint like Jiffy Lube.
Also be aware that your car is now 6 years old, which for a normal car is fine, but for a German luxury car means you are now entering the wallet-draining phase of ownership. Expect expensive problems from here on out.