For those that do your own oil changes, you can get a 3 pack of 1 gallon Rotella T6 5w40 for 51.69 (and free shipping) and there is also a $21 rebate through Rotella. Amazon has it for $61 and change for those that do not have Sams Club. According to the rebate site both are participating in the rebate.
Sams Club:
https://www.samsclub.com/sams/shell-rotella-t6-5w40-synthetic-heavy-duty-diesel-engine-oil/prod22303277.ip?xid=plp_product_1_5
Rebate:
https://rotella.shell.com/coupons-rebates-and-sweepstakes/better-fuel-economy-meets-better-wallet-economy.html#iframe=L2RpeS9uYXRpb25hbDE4Lw==