New engine issue

[elorenzof]

1969 camaro 327. New build. Stock build. New carb edelbrock AVS. New EVERYTHING. (i know we can still get a bad part) Engine was rebuilt by a reputable engine shop here in phoenix.

We installed the engine, got everything filled and hooked up and proceeded to do our initial 15 min break in.

We had timing set to about 13 degrees BTDC. we were happy. Car ran great for about 5 mins. Then stalled. we tried to start again and it ran like dookey barely. The timing is now about 20 degrees BELOW the timing tab. let it cool off and try again this AM. Car started perfectly fine and ran great and we double checked timing. It was back to normal? so it ran for about another 4-5 mins and stalled. Now trying to crank the timing is WAAAY off again. Im betting if we let this cool down again it will start fine again. Can someone please help? 2nd new distributor just in case it was a distributor thing, same thing. the distributor is not moving, it is nice and snug enough to turn only for timing issues.