Getting a clunk from the rods, need help

I have an 86 1 ton with a 360 in it. Completely rebuilt the engine. Bored .030 over, new comp cam, 9.5:1 pistons, HV pump, crank turned .010 and .010. We started the engine and it runs strong and revs nice and quick. Everything was broke in properly with no issues.
The problem I am having is that at a low idle I can here a bottom end knock that goes away when revved up or driving. I drained the oil and pulled the oil pan. Everything looks good and clean, but if I grab a hold of the rods, I can move them front to back making a similar clunking noise. All rods are tightened to torque specs and not loose at all. I get no up/down movement. Just the front to back. Anyone know what could be the cause of this? Is it possible that it is a machining issue?
Thanks for any help