Wierd massive timing reduction intermittant on Vortec with LS1 pcm

[4wheelin]

I have a customer who's been chasing a fault where intermittantly the timing goes massivly retarded, into the negatives, we have replaced cam/crank sensors, I have done a relearn with a Snap On scan tool and the cam error is 0, when not faulting the car runs very well, it has a cam and heads in it. The LS1 ecu is using a van calibtation. I don't know if I've missed something in the tune, we don't get many of these in Aus, it seems to happen from startup intermittantly and sometimes a start stop will rectify it.
I've attached the tune and am open to any suggestions.

[slows10]

Post a log. Base spark tables look a little strange.There is a big dip in the 400-800 rpm range.They are to far different then B5913-B5914. B5915 imo is to low.

[4wheelin]

I have set the idle timing low at 800 RPM as it makes the engine more stable at idle due to the camshaft, it gives the pcm lots of room to move to add timing to prevent stall. I actually don't have a log of the vehicle when playing up, the customer has a generic scan tool and checks that, when the car plays up the timing will be very low or sometimes even negative and the power is significantly lower, it logs a crank cam fault but both have been replaced and set to 0 error on the cam, I was thinking a wiring fault but the pcm is commanding the reduced timing, I don not know if that would be the response to a cam sync or crank sensor issue.

[haulinit]

Its a long shot, have they checked the cam gear for knife edging or slop?

[4wheelin]

No I haven't, the problem seemd to start when the cam and heads went on though, I have repeatedly checked the cam sensor offset and it appears to be correct at 0 where I set it.

[haulinit]

Sorry the Dizzy gear for knife edging not the cam gear.