i had a friend in my truck a couple weeks ago and it started shaking. he asked me if i had ever hit a curb, which i did awhile back. three people in these things aren't a good idea. i don't ever remember it shaking before i did hit a curb. but anyways he said it could be my alignment. i believe my dad said something about it as well. once i get a job i'll have the alignment checked out. i am waiting on a call back for a second interview right now.
EDIT: didn't mention that i noticed my right tire has been low for the past week and my truck hadn't been shaking at all while that tire was low. i decided to head back to my house before i drove out of town a ways. filled it up and once i reached 40mph the truck started shaking again. i'd stop and go again, and it shook every time i reached 40mph. i did that several times. and then i got back on the freeway and it didn't shake. last time i reached 40mph before i returned home.