I also was in the Post Falls Wal*Mart a few days ago and saw the shopping carts with the closeout of Rotella synthetic.
This oil will be OK for you in the summer, but what's the advantage for you? If you stick with normal oil drain intervals, the $2.50 cost per quart is no bargain, and the oil won't work better for you than any good conventional oil. This diesel 5W/40 is a big help for diesel engines in cold winters.
Ken