Shuddering front end...

[Luna X]

quick thought...

have you recently had to get on the brakes really hard? Excessive heat could get a rotor out of true and just be felt at certain speeds almost like a wheel out of balance.

[Big G]

How old are the tires? Sometimes the steel belts will delaminate and shift which will cause a shudder or wobble especially at low speeds. If you jack up the truck so you can spin the wheel. Look at the spinning wheel directly at the tread and sometimes you will see the wobble in the tire. Just a thought.

[Triathlete]

I have 2 sets of tires...does the exact same thing with both.

[etlsport]

it could be a bearing, but you should feel that while doing a shakedown of the front end. you would also probably hear something

any play in the front propeller shaft?

also check the brakes. if you have a stuck caliper, a warped rotor would give you that vibration/pulling under moderate speed, but once the brakes are applied or you are going fast enough, become less noticable