Tight 383 Cam Bearings

Rusty hit the nail right on the head, Chrysler machined the front three cam journals first, the rear two were machined after from the rear so there can be some issues like you are experiencing this requires newly installed cam bearings to be "broached" like what Rusty explained in his post.
Rusty does indeed have knowledge most others do not.

If the problem is misalignment of the bores, the "grooved camshaft" trick is great. If the problem is a cocked insert, then you are simply compensating for a problem the installer created.