383 rebuild - kinda whimpy on the dyno?
You have something wrong somewhere. 0015 is a little tight but would not cause what I see. I've ran as tight as .001 on stock cranks and never had a bearing problem, but had some easy break in time after cam break in. If I have a crank turned I shoot for .002 to .0025 on rods and mains. A lot of them old speed pros call for clear down to .001 clearance. No way I would go under .003 even if it called for it to be .001to.002. I had built an engine with .001 and it locked up after cam break in. Just to much heat on break in. Scuffed the walls pretty good.