I'd like to see both the cam cards if you can?

A vacuum gauge, mechanical! Is also a useful tool to look for shake in reading. Won't find it in a log... is vacuum steady at idle? No shake in reading? Accelerate and differences should be smooth, no shake.

There was or still is a 290 HP 350 Chevy engine that just sucked for idle and by specs should not been that bad. There's always a degree issue when installing a cam, or at least check and see how far it's off? Push the cam specs to .224 duration @ .050 and this degree is more crucial with idle!

Or who adjusted the rockers?

15" of vacuum is easily tunable if it's a steady vacuum. But 15" of vacuum could be 17 or 13 depending on elevation.