01 Dodge Ram slight vibration

I have a 2001 Dodge ram 1500. 5.9L about 170,000 miles on it. My problem is frustrating, because it doesn't do it all the time. When I am stopped on a hill or about to make a turn and when I go I feel a vibration in my seat. But it only last about 1 or 2 seconds and then everything is fine again. I would like to hear anybodies input on this, so I can try to fix it before it leaves me sit. Thanks. TIm
If automatic - check transmission fluid for level and color. Read exact instructions in owner's manual - it probably gets checked running in neutral.

Other: See if u-joints are ok, transmission mount. May want to get some help if you aren't sure just how to thoroughly check these items,