New symptom today. Not entirely sure how to describe it, but I'll try and start from the beginning.
I haven't been able to get to pulling the IP/valley pan/valve covers/rockers/valve springs due to the weather. Instead I've been dealing with a strange charging issue. 200A breaker inline with the charge cable from the alternator started tripping repeatedly after attempting to do my compression test and installing the 6.0L glow plug harnesses. Issue with the compression test is that the needle would only bounce to 200psi on any cylinder and wouldn't hold pressure (bad gauge). After putting everything back together and installing previously mention GP harnesses, the breaker would trip and not allow a manual reset (like it was still too hot). I replaced the alternator and it wouldn't charge above 14V at anytime. Nothing has changed with any of my grounds, but I'll be adding one to the back of the 3G when I can. I pulled the regulator harness and cut out the crimp connections and soldered them, swapped the leads on the breaker and tightened the belts more. Might be alright now.
But here's the part that's relevant to this thread...
When I started the truck, everything seemed normal (normal cranking time, normal plume of white exhaust, normal high idle), but then there was this strange, almost stumble/pop or burp (not a backfire) and the idle smoothed out even more. Maybe it wasn't hitting on one cylinder? Didn't shake or sound like it does when loosening an injector line while running. I'm still leaning towards worn valve guides or a sticky valve, but I guess it could still be a collapsed lifter? First thought was sticky injector nozzle, but they are Russ' rebuilds and with the inner occurance of the "gulping" and one occurance of chuffing, I'm doubting it's an injector.
I'm going to have to do balljoints, tie rod ends and alignment before I can break into the top end. Driver's side is getting bad from where I got hit (and didn't have any "proof" that she messed up my balljoints and TRE's).