Spark knock or something else??

I have been battling an interesting knock under high load low RPM, only under acceleration.

New coil packs, spark plugs, fuel pump is fairly new, fuel pressure is consistent at 45 to 47 PSI idle and when accelerated under no load, no vacuum leaks and no electrical faults or codes. The fuel trim values are perfect while driving at any road speed.
It's as if it rattles/knocks at high engine load.

I did shoot some seafoam through it earlier today and it cleared its throat of a low idle issue but the rattle/knock persists.

Any ideas would be helpful.


Engine mileage is 197k.

 

I think the problem may be you are pushing the engine at a low RPM. Try downshifting.

 

The truck has ran this way for years but never had this spark knock or whatever it may be. Its also an automatic. It will do this at low RPM and high load but not at any other combination.
Stabbing it from a dead stop will create the knock as will attempting to accelerate from 45 to 50 MPH. Once in the higher revs no issues.