Clunk noise when shifting upwards

Does your car have a shift improver kit installed? A lot of shift improver kits cause it because they raise the line pressure. It won't hurt much. Little hard on U-joints but that's about it. What's happening is when you let off the gas the 1-2 shift hits taking up the slack in the drivetrain. If you back off the throttle pressure linkage adjustment a little it should help some. The only drawback to that is you may lose kickdown at highway speeds.