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Closely look at the spark plugs for any cracks in the porcelain, inside and out.
Get an infrared temp gun (very cheap at Harbor Freight), while idling and about 1500 rpm, aim it at each header tube. The temps will be very obvious to which cyls are misfiring.
If the plugs are good, and the timing gear was installed correctly with the dots lined up...I'd suspect wrong push rod length is holding a valve or two open.
Call the cam company... does it use anything other than stock base circle?
Were the heads decked? (if not, why not?) (always do at least a clean up pass on alum heads while off)
If either of those questions are a Yes answer, the PR length will not be stock. But...just a guide, still need to measure for every build. I've seen cams that they swear are stock base circle...are not.
What did your rocker nut turns end up at? lobe on base circle, turn rocker nut down to zero lash... then how many turns to TQ spec? You mentioned 1 1/2.... that sounds like too much if that is what actually ended up with. 3/4 to almost 1 complete turn is usually close to ideal. Or more accurate is to use a Comp Cams PR length checker.
The other thing you can do is take your compression gauge hose and put a compressor fitting on it to pressurize the cyl that is misfiring. With the cam on base circle for both lobes pressurize the cyl... anything blowing out the exh or intake? Yes...too long a PR if that blowby stops when loosening up the rocker. The blowby continues after loosening the rocker...bent valve.
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