By “front end checked” what does that mean? Did the tech check for damaged brake rotors, or loose wheel bearings or failing CV joints or loose steering or damaged bushings or all of the above? Was the rear checked, too? Sometimes and issue you think is at the front is really from the rear. It sure sounds like you threw a (big) wheel weight off at speed. Always consider a “horse” before a “zebra” but you said you had the tires balanced… all? or just fronts?
Have you had the engine itself checked? Are all the drive belts in place? Loose alternator, loose power steering pump? Loose air conditioning? Does turning AC on and off make a different? Did you shift the transmission down into a lower gear so the engine revs higher? Did the vibration change?
Driveline vibration changes with car speed, engine vibration changes with engine RPM, transmission does both (manual trans or automatic?)
There just isn’t enough info to diagnose it without a little more help on when and where it occurs. Post here and we’ll try to help.