If you have an Advance Auto around, there is a good deal on Rotella T6 with coupon code DOW9 (30% off) and a rebate too. rebate only good for one or two gallons however. You can see it HERE.
Steve

 

That particular deal expired. Here is a LINK to some other coupons. The code RETMENOT124 is better is you buy 5 gallons as I did, wish I would have seen it before! 5 gallons for $74.95 before tax! 4 gallons for $66.96.
Steve

 

$5 off per gallon of T6, limit two gallons:

Shell Rotella T6 Rebate - Shell Rotella