Front end vibrates when braking at high speeds. Does not vibrate at low speed. on 2006 Chevrolet Equinox

We have replaced/inspected brakes, different parts in the front end, etc. Husband knows all about cars/builds them. Called the Chevy dealer and they did not know what it was about and had an Equinox in the shop with the same problem. No codes. No lights. 210K miles on the car. I am wondering if the ABS needs to be reset/replaced because one time when braking it bounced back like the ABS was active and the shaking was a lot less and now it is back to shaking a lot.

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3 answers 4 comments
So i guess the tires have been checked for out of round and balance. Brake rotor run out checked, does it do this ONLY when brakes are applied?
Yes to the tires and brakes - all checks
Only happens when the brakes are applied and only at 55 miles per hour and above. Does not happen at 50 and below
Got me, it is a mystery! Just dont drive over 54 mph.
have frt brakes ck and mach rotors.when you did the frt brakes did he repl pads only or pads and rotors? what quaility were they? dealer,auto zone or what?
have done it several time. My husband does it and he builds street rods so.......yes!!!
whta quaility of parts is he using?
uneven tire wear, brake rotor worn out, brake pads. mismatch tire these can possibly cause vibration.