Loud humming noise from front end

I recently purchased a 2001, 4x4 GMC Jimmy with 35K miles on it. On the interstate, it began making a loud humming noise coming from the front right wheel area and as I decreased speed, the noise became slower and lower in pitch. I took it to a dealership and had the front right hub assembly replaced. That did not solve the problem. They replaced the front axle. That did not fix it either.

Can anyone help me?

It may be the driver's side bearing and the noise is traveling... I would also look at wheel balance or even your tires may be worn funny. Have your alignment checked.