1992 22re 4x4 pickup

In the past 6 weeks or so, I have noticed a fairly significant pulsing sensation when applying the brakes. I do not feel it in the steering wheel. The brakes do not pull in either direction and seem to be as strong as they should be. The front brakes were replaced less than 10,000 miles ago (pads, rotors, and one caliper). Rear brakes look to be fine. At first, I only felt the pulsing when braking at highway speeds. Now, I pretty much notice it at all speeds. The pulsing slows as the vehicle speed slows.

I know warped rotors would be the most obvious culprit, but based on when they were last replaced, I'm wondering if it something else.

Thanks for your help.

 

perhaps uneven glazing? or just a bad set of rotors poorly made