98 s10 rear clanking and vibrations?

I have a 98 s10 that I recently drove from florida to ohio.On the way up,I started noticing a noise from the rear end that sounds like metal on metal at low RPMs.Yesterday,we took her up on the highway,where I all off a sudden,got bad vibrations at high RPMs.The problem seemed to escalate as we kept driving.Im lost here.THINKING rear bearings..?Also,is there a grease fitting for the rear end?I used to get my oil at Wallyworld,where they claim to grease the wole rear end,but I dont use them anymore after they screwed me more than once on oil changes,so I havent greased everything myself in quite awhile.So,does it sound like a grease problem or something in the rear end itself?ANY help would be GREATLY appreciated...Nothing like being in a new place,only to have truck problems now :(