Hey I'm a long time reader of the site but never always answered my questions by reading others posts. After reading several posts from other members I'm still uncertain. I have an 06 Silverado 5.3 with 178k miles. Owned since day 1, mostly highway miles always serviced with M1 5w30 an Purolator or M1 filter every 7-8kmi. During my last oil change I considered switching to a different grade oil due to 1) Burning considerably more oil. I recently added an entire quart of oil after only 3k miles. 2) Typical GM 5.3 cold noisy startup issues. Sounds similar to what others have called 'piston slap' and valve tick, etc. 3) Am I using the best oil for my needs or for my next oil change would M1 high mileage be more appropriate? For these reasons I considered switching to M1 high mileage formula and possibly a thicker grade oil. Switching to M1 0w-40 that I had remaining from a car I no longer own. Comparing the Phos./Zinc levels published by M1 the "European formula" I used in my VW car I figured it might be a nice bonus. I read where the 0w oil eased the cold startup noises on other GM 5.3 owners trucks and also knew several people running a 40-viscosity oil in high mileage oil burning engine with success. Unfortunatly I couldn't find much in people that formerly used 5w30 now using a 0w40 oil. I am an engineer by trade and after doing some research into the specs I decided to go ahead and change my oil using the 0w40 euro I already had in the garage over the high mileage oil. I am currently traveling each weekend 750mi round trip towing a trailer moving my girlfriend from college and selling a house so I figured it couldn't hurt using the higher viscosity oil. I currently still have the trip home to observe but so far I have noticed my oil pressure gauge seems to run higher than before. As in a few pounds higher, not much currently the needle rests nearly touching 40psi at idle(with 0w40) where formerly it was a closer to 36-37psi. While driving, I haven't noticed yet. My concerns are 1) Is this oil too thick to allow for adequate flow in tighter tolerance areas? 2) Would the M1 high mileage have a better additive package for my needs despite having a lower zinc/phos. content that the euro oil? 3) Does this higher viscosity result in considerably higher oil temps? I was hesitant to think any additive package would reduce oil consumption but M1 high mileage mentioning doing so on the bottle made me feel it may be better suited for my application BUT M1 doesn't list any oil specs stating the additive properties other than zinc/phos content. Shown here: https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide.pdf With all the interstate/towing mileage I plan to rack up on the weekends while selling a house I plan to run a 10k mi oci this time. I've been wanting a chance to submit an analysis and this may be my best chance. My typical 8k mi oci is limited due using a company car so I feel that short in town trips cause too much moisture build up to take this oil the milage its rated for. I know it doesn't effect my lubrication requirements but I run a 93 octane tune along with an Edge CTS display to monitor engine parameters, unfortunately oil temps are not provided. I do understand a higher viscosity should theoretically lead to higher oil temps for several reasons but was unsure if the oil cooling system alone prevented oil temps from varying much regardless of oil grade. Thanks for the input, I rarely post if ever but I frequent the forums on a weekly basis.