starts shuddering at 50 mph its really bad at 60 mph then when you get up to 70 mph it goes away. i did u joints its about 1500-1900 rpm it is shuddering at any suggestions

 

Did problem start after or before you did Ujoints?

 

its been there all along since ive had the truck

 

Could be tires, or driveshaft. Balance the tires first then if still there have driveshaft checked out, could be bent or out of balance. Ujoints not center in yoke properly. Two piece driveshaft or one, if two piece might not be indexed properly.