I have been using mobil1 10w30 in my 2000 chevy 6.0 v8 and it seems to be too thin for my application in this 90deg weather. I just put 15w50 in but i don't know if it is too thick for my truck. I could go with mobil1 5w40 but I found 1 gallon containers of Rotella 5w40 synthetic for $6 and change at advance auto.. Would the Rotella be a suitable oil for my truck? I usually run 10k between oil changes with the mobil1. thanks!