This weekend I changed my oil from standard 15-40 to shell Rotella 5w-40 full synthetic.
Right from the start I notices my engine was much quieter. After driving about 100 miles, I noticed my milage had gone up by almost 2.5 MPG. That was with the dooohiiiky in the roof, however if this looks good after a few tanks..... I'm sold! I'll never go back to regular oil again. I did have it done at Wal-Mart for about $75.00.
I did however have to make them do it over again because they put regular Rotella in the first time. Make sure they use the blue bottles not white ones. They weren't to happy about having to drain 15qts of new oil. Oh-Well the techs should read the work order first.