Nash, duzn't sound like you had a good weekend, I had a old GMC jimmy that kinda made the same noise as you stated and it turned ot that I droped a lifter but I never drove the truck down the road as you mentioned it would clear up at cruising speed. Either way look on the bright side, this means you get to go grab a few 12 packs and call the friends up for a good evening of turning the wrenches.