Hi guys, just wanted to give a small update here on my choice to run an OCI of the Valvoline Premium Blue 15W40 in my 05 PowerStroke 6.0h. To recap, I've ran mostly 10W30 Rotella in this truck and its been flawless. I used to live in Northern VA and knew the thinner vis oil would help cold starts. Now that I live in central Florida I figured I could go back to the 15W40 with no issues. WRONG!! I can seriously "feel" the truck is more "sluggish" it starts harder and is not as smooth until it warms up. I never dreamed that minor viscosity change would make so much difference in this truck but it did! However, interestingly enough I did notice slightly cooler EOT's (oil temps closely monitored in the 6.0's and I'm adamant about watching gauges) Average temps with 10W30 on flat high way has always been ~199-202* and with the 15W40 in there I'm seeing average temps of ~197* I'm going to take this OCI to 5000 miles and dump it for some 10W30 again unless I can get my hands on some of that Delo 15W30 SD.