Pennzoil used to be a four letter word, and i believe the conventional still is as it is s wax base. Any full synthetic will give you decent results although I've done a ton of reading over the last week to decide what to use, the last 30k miles or so I've used white bottle valvoline, now I'm switching to the syn power valvoline full synthetic in 5w30 and the motorcraft 820 filter. The filter has a check valve to keep oil in the engine to reduce dry starts. Royal purple is good and neck and neck with the syn power and Pennzoil ultra but costs much more, i ran it for 10k miles and didn't notice any real difference. My order comes tomorrow because Amazon has the best price, 17 bucks cheaper than orellys per 5qt jug. I'm hoping the filter helps with valve noise on cold starts.

 

While the varnish is a bad thing, history on the forum shows that most of the time the tensioner seals blowing out is the biggest cause. Seal blows, oil pressure suffers and the phasers are one of the last things to get oil. They then don't operate correctly and cause the chain to slap which then breaks the guides. Pieces of the guide then plug up the pick up tube and lead to even less oil pressure which then leads to the phasers breaking.

 

you have a bad cam phazers… they are located the front of the camshaft, and controls timing and fuel econ.. you can have them replaced for agout 6 to 8 hundred.. or you can unplug your cam solaniods they are on the front of your valve covers.. this will stop the engine stumble @ low rpm. note you will get a check engine light and your fuel econ. may suffer a bit. If you live in a commy. state like I do (mass) and have to hand the state 29 dollars a year for a insp. stic. just plug the cam sols. back in @ sticker time, them go to your locale auto world an have the counter guy or gal remove the light. Go get you sticker then unplug"em again THIS WILL NOT HURT YOUR ENGINE JIM

 

Alternate thought: Fuel/Spark system.

Cold start, the engine is running mostly open loop, off a program. Once it warms up, the fuel leans out and gets harder to light. Inconsistent injectors or ignition can make life miserable.

 

Ask a Mod to move it for you. Nice truck BTW.