I've been running Castrol Agri-Power Plus 15w40 in the Cummins 4BT's and the Multifuels for years. Meets the same slew of Cummins/Mack/Cat/Milspec/API ratings as the Rotella and others mentioned in this thread. Not only has it been a dollar a gallon less expensive at Agri-Supply, but it is supposed to have a tad more detergent and stabilizers to be more friendly to agricultural use-run hard for a week or so, then bassically shut down till next season (we've got some equipment on the farm used just like this...). Figured that it was similar to how I drove my trucks, hard for a week or so, then no activity until next month as I worked through the rotation...
Went into Agri-Supply in Garner las week, no longer had the Agri-Power Plus on the shelf, had the OTR Castrol 15w40 instead, at a dollar more per gallon than the Rotella... So, I got Rotella this time...
FWIW: The drum price of Rotella a Sam's Club is about the same as the Agri-Supply drum price...
FWIW2: Coworker told me this morning that she used to work for one of the oil/lubrication wholesale firms in town and chided me for buying this stuff retail since she could "set me up with her old buddies..." We shall see...