Odd timing problem 360

I have an odd problem with the timing on my 360. Rebuilt 360 .30, Stock heads with valve job, comp cams 942 springs with lunati 402 cam and lunati lifters, new harmonic balancer.

My timing mark jumps around starting at about 3k and up. New timing chain, I have tried 3 different distributors (2 stock and a billet) 2 different MSD 6als. Changed out the oil pump from a high volume to stock. I am running out of things to check.

Now sometimes right after it first warms up I can rev to 6500 and the timing mark looks ok or 4000 rpm but if the engine runs there for more then a couple seconds the timing mark starts bouncing.

I thought it might be lifter pump up but I am using brad penn 10w-30 and a stock oil pump now.

Someone throw me a clue please?!?

Thanks,
Dan...

ps. using a craftsman dial back timing light a Taylow 8mm plug wires (also tried with a set of the MSD 8.5 wires.) The same timing light on my brother's engine shows a rock solid timing mark all the way to 6500. He is using a smaller Crane cam.