I didn't use any DI cleaner on a regular basis. I wasn't aware of the amount of carbon buildup until I removed the intake manifold. A leak down test confirmed compression loss in cylinder one. After removing the head and cleaning it, I removed the rockers, springs and valves. I replaced all 8 exhaust valves, they were pretty bad. I then ported and polished the intake and exhaust ports and combustion chambers. I lapped the valves which went okay, but I still had leakage in cylinder one. I am trying my best to not go to a machine shop. I ordered 4 new intake valves which should be here tomorrow. In the meantime I pulled the CAT, and removed the waterpump & thermostat to install new ones. Hopefully the new intake valves will seat correctly and I can start putting everything back together.