it's the craziest thing.. it doesn't sound like valve train to me either, but I've never heard anything knock like that when cold and go away. any time I've been around bottom end stuff, like main or rod bearings they all get much worse than hot.. can almost sound OK when still cold on thick oil.
possible it's a stater rubbing the flywheel? or balances that's completely come part? I'm so confused by this truck.. cold, 40psi oil pressure and it knocks, gets warm, drops to 11 psi and gets quiet.
I got nothing.
one of my first engines I build as a kid, I added a windage tray and didn't get a clearanced enough a rod hit it. that's the closest thing I can remember hearing to this.