I changed the oil in the truck today and while I was under, I noticed I could rock the driveshaft back and forth ever so slightly. Does anyone know if this is normal or if it is a bearing or... Thanks guys!

 

Front to back?
Side to side is normal, backlash.
Play between ring and pinion.

 

I rotated the shaft (right out the back of the trans) clockwise and counter-clockwise and it had about an 1/8-1/4" play.

 

normal condition. as stated above you are moving the backlash between the ring and pinion gears. without that there is tension on the gearset all the time and you would end up with some bad juju. while doing that however, watch the ujoints. if you see part moving without another part..... time for new ones

 

Cheers