Spun Rod Bearings

I have a 99 cobra. I have recently rebuilt the motor, Twice, and both times I have spun the rod bearings. I built the first motor myself and use plenty of grease on the rod bearings. The second time the motor was built my Mcallister Brothers Racing and it too spun a rod bearing. I believe all the clearences were within spec for an aluminum motor. Has anyone had this problem and if so what can be done to prevent another spun rod bearing.

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The first time I just got done installing a set of Probe pistons and Manley H-beams. I used a lot of the bearing grease. Had the mechanices install the engine back in and they started it. Upon recieving the car I started it and heard a rattle. Asked what is was and they didn't know. Over time it got worse and worse. Finally stripped the motor down and found that it was a spun rod bearing. Second time, still not sure what it was I had mcallisters build me a motor. 03 cobra cams, probe pistons, H-beams, DSS retainment system, Got and intercooler and blower. Had shop install the motor......upon recieving the car I started it and I can hear same rattling sound that was present when rod bearing was spun. I don't know what is going on. Oil pressure at idle is at 40psi and 75 under load.