^^ in your case i think it's the wheels themselves...

I still feel wheels are fine that's my last concern

I will start from re balancing with road contact figures.

I just got new tires for my 370, same kind as before, nissan says they are balanced, but the wheel now shakes from 75-80mph (or the whole car kinda i can feel the gas pedal kinda knock) and it also shakes when i brake from 50-60mph. It's driving me crazy to have it drive like this now when it was so perfect before the new tires. Why can't the dealership fix it? For expensive performance tires, it's frustrating to think they are at fault.

did you try get your lower control arms checked?

No, I will have them check that (and anything else i can find that could be the problem), mostly they just give me a runaround. This site has helped me before with the dealership with a high pitched noise issue, it was a recall on the car's computer. But thanks for tip i will try anything, i loose sleep over these things :-)

Sounds like one of the wheels isn't centered on the hub properly. I would suggest (again) to simply take the wheel off and remount it, making sure you are supporting the wheel when you torque down the lugs *in proper order*.

Before doing this, you can also just check the tire pressures to see if there's any weirdness.

what type and size of tires you running?

I had to drive with the dealership tech, and insist they over torqued my lugnuts, making the rotor off. They spun my rotors and road forced balanced again, so after three times going back to the dealership, the shake finially went away. MAKE SURE WHEN YOU GET NEW TIRES OR THEY TAKE THE WHEELS OFF, THAT THEY USE THE TORQUE SPECS WHEN TIGHTING THE LUGNUTS or your wheel will shake while braking and from 60-70. It still isn't perfect but I'm tired of spending my time at the dealership about this issue.

I'd go somewhere else next time you get your tires changed. I've been goint to Wheelworks for years taking wife and in-laws cars there too. They've made a lot of money off me but I don't think they've ripped me off yet. My wife thinks it's better for a woman to have a man there as backup. Even better if he knows something about cars.