96 S-10 Blazer vibration noise

I have a 1996 small 4wd Blazer Vortec that is making a low pitch humming noise and vibration when you hit 60 to 75 mph. At 80 mph it stops. You don't hear it below 55 mph. I just did a 4 wheel thrust alignment on it yesterday for $100 along with a 4 wheel spin balance and it didn't help. It's really a low pitched humming aggrevating vibration and loud at speed and makes your ears hurt and mirror vibrate so bad that you see blurs in it . If I throw the truck into neutral it still does it when rolling. I try to turn up the radio so i don't go nuts or drive below 60 mph. I can't take a trip with it at all on the highway because my family complains of the noise. I'm running all season Goodyear Wranglers on it. The Chevy Dealer said it may be a universal joint but I had it changed in January when I bought the truck. Any help would be appreciated!! Thanks, Scott