Lopey idle when hot

[PAvector]

After the motor is hot at normal operating temp, it sounds like a big cammed big block motor. Lopey idle. It’s not all the time, maybe 60% of the time. The other 40% of the time the sled idles fine. Sled has 25k on it and valves were shimmed about 12k ago. Don’t think it’s a valve clearance issue, not the same symptoms as cold starting issues I had before shimming the valves. O2 exhaust sensor was changed and gapped the plugs with no symptom change. The sled never stalls. Any thoughts on what to look at?
2014 VIPER 137.