Did you just have front tires mounted? Are they installed out of round? Look at the bead and see if it is uniform.
I had a Volvo one time that had tires mounted incorrectly, and had to have them both redone to stop the vibration, but it was not violent.
If they are not wheel centering pilot hubs, one can put a dial indicator on the front tire and loosen lug nuts and usually get enough movement on lugs to adjust out of round condition. Put high spot up top and let wheel drop when loosening; repeat.
Do you have a busted cord on a tire….
A broken spring shakel? Kenworth one time broke a shakel coming up to a light not going more than 20 mph….