wierd drivetrain problems

I have a 1990 Chevy 4x4 1500 (manual trans). I took off and I heard a loud metal clang in my drivetrain around the middle of the truck. I stopped and looked but no visible driveshaft problems. Took off and noticed when I turn there is some noise from the front and It feels like the truck bogs down like something is pushing on it. Took it home and inspected the whole drivetrain: Driver and Passenger half shafts, front and rear driveshafts, all u-joints and no visible problems. When I back up and go foward I hear the clang in the middle, but the problem when I drive feels like it is up front and some noise up there as well, only when I turn. If I drive straight you really cant tell but the motor rpms go up and down about a 100 rpm like something is pulling on the motor a little. And when I stop and go foward you can hear what sounds like driveshaft play. I am confused any suggestions.

Take a look at this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=262226

//2000CAYukon