2004 GMC Sierra 1500 lm7 tuned with hp tuners from very reputable local tuner

P0300 code only at idle I have replaced near everything
both 02 upstream down stream tuned out
plugs/wires
tried different coil packs from good running vehicle
Took off heads inspected all valves cleaned and reinstalled.
new cam sensor
New map sensor
Different maf sensor
Cleaned throttle body
New intake gaskets
Had tuner look at the tune
I'm stumped
Also done compression check before removing heads all were in a 5 to 10 psi of each other.
fuel pressure 58 at idle does not increase if I run it to 2000 rpm.
​​​​​truck drives so so it only seems to set a code at idle sometimes want ms to backfire through the exhaust if it sits for a bit but not always
where to check next I'm going crazy and broke quickly