Checked your timing gear?

Here's the deal. Mopar put the cam much higher in relation to the crank than chuvy did. This is good when you want to build a stroker as there is more room for crank throw but bad in regards to chain stretch.

Comp Cams double rollers stretched noticeably after only 5K miles. Cloyes did after 15K but not as much as the Comp. I use a tensioner now on all my LA builds and my timing is much more stable, but the cam timing (and ignition timing) will still vary with use but the slop is pretty much eliminated. If I were to build a strip only Mopar with very high spring pressures, I would go with a quality gear drive like a Milodon.