LS7 backfire initial startup E39 ecu

[TANKMASTERJ]

Ok guys here we go. LS7 with Late model racecraft cam and heads. Purchase out of a wrecked Z06 2008 model.
I converted to wet sump so I changed the timing set to a Katech while there and a melling high volume oil pump. Using a psi swap harness HAR-1037 and the gm E38 ecu that came with the wreck.
I got 59-60 lbs of fuel pressure.
It backfires a few times the first time I tried startup. Thought maybe the intake was sucking air since a smell a little fuel I think. ( My sniffer sucks since covid) but so I tightened intake some more. It fired up and sounded smooth at about 1500 then one more backfire.
I haven't scanned yet because my tech 2 was at my town shop and I'm home.
Any suggestions to start trouble shoot.
I'm new to LS but hot rodder and heavy quip mechanic for 30 years.
Advice needed.