you probably have some worn front end parts, ball joints tie rod ends ect.
id check the front end for play in the joints or take it to a shop and have
it checked out.

I think you were supposed to do some service on that front end about 60,000
miles ago . . . .

Sounds like worn parts...Rag joint/u-joint, ball joints, drag link, tie rod,
steering gear, etc. (I don't know the steering components on this truck, so
sorry if I mention parts it doesn't have).  To find the suspect components,
you can jack the front end and place it on jacksstands with the wheels free
to turn, secure the steering wheel (the steering lock may not have enough
strength to hold it and will have a little play, so instead use a couple of
lengths of rope to secure the steering wheel), then push each wheel left and
right and look for any freeplay in the steering components.  Having someone
the help move the wheels while you look will greatly easy this diagnosis.