You say there's no detonation but that it's dieseling? I bet it is detonating but you can't hear it. I run my 5.9 with 93 octane. My cam is a little smaller, at 222/228, on a 107lsa, but I'm also running thinner than stock head gaskets and have heads shaved .030 to bump compression to 9.5.

I'd consider at a minimum to try 89 octane and see if it makes a change.