Whats up with my brakes ????!!!!!!

[zipgun]

I have a 1990 V1500 4x4 Burb with 124,000 miles on it. It has a developed a weird shudder in the front brakes when it has been driven awhile - aprroximately 20 minutes. I have replaced the brake hoses, pads. The rotors dont look warped and arent gouged. Has anybody else experienced this? I can drive it for the first 20 minutes and it stops fine but after that it shudders and bounces a bit. I have bled the brakes as per the manual and am sure there is no air in the lines. I am stumped at this point.

ANY SUGGESTIONS ?

Thanks,

zipgun