Hemi piston slap?
I own 4 late model hemis. They all have differing levels of valvetrain noise from zero, to near THAT when cold. I have never heard hemi and piston slap in the same sentence. I do hear lifter complaints, although I have never had any real problems
Mine are..
36000 miles
78000 miles
109000 miles
197000 miles
Put a quart of Lucas stabilizer in it to displace one qt of oil.
Bet it helps. Easy $15 test