Carbon build up in the combustion chambers is a common problem when you baby an engine too much like that. It can cause reduced performance, knocking, and/or pinging under acceleration.
It's time to do the old time-honored "Italian tuneup. When and where safe, start doing hard full throttle accelerations to high rpms, 4k and higher. It could take time to get it cleaned out, and don't be surprised if you see bits of black gunk blowing out the exhaust.
And when you can, start driving it more aggressively and stop babying the engine. It runs better when it sees higher rpms to keep things clean.
I learned about this from a Corvette mechanic. He said few customers drove their Corvettes aggressively enough and would bring them to the dealer complaining it wasn't running right. He would repeatedly rev them hard until they were running well again.
The reason engines start knocking or pinging when the combustion chambers load with carbon is because the carbon reduces the size of the combustion chamber which raises the combustion chamber pressure during the combustion stroke which prematurely ignites the fuel causing knocking or pinging... aka premature detonation.