6.0 or 6.6

[Colossus]

$12.00 for a 2 gallon jug of Blue DEF from Pep Boys. figure you need 4 gallons to fill the DEF tank up so $24.00 to fill up the DEF tank. DEF Tank lasts about 5000 miles if what I'm seeing with mine.

[Cowpie]

I would be less inclined to buy it in jugs unless I was desperate. DEF has a shelf life. Better to get it at a truck stop bulk distribution or commercial truck dealership like I mentioned. Far cheaper, higher volume dispensing that ensures fresher product, etc. These SCR units are darn finicky about DEF quality. Once things get goofed up, it is a major hassle to get them straightened out. Usually tank has to be flushed, lines flushed, and new DEF filter, and at worse, another DEF dosing injector.

[Colossus]

No decent truck stops around here for about 30 miles and I am never on that side of town, otherwise I probably would go fill it up there, it's a good idea like you said. I check the dates on the BLUE DEF stuff I buy. Have yet to find anything older than 2 months, that is if it is not filled up at the Dealer or at my service shop during an oil change.