Optimas are not what they used to be for one thing , ever since they closed the US plant and moved to mexico and went to making them from used innards. Even optima knows it as they no longer warrant the things for 6 years, its 3 years now and you'll be lucky to get that out of them, I had 2 new ones croak in about a year in a couple of my cars here recently. Aside from that they may have the amps, but they are woefully low on reserve capacity which is what a diesel really needs on those nasty cold mornings, it's the high reserve capacity of commercial batts that will get you those extra cranks to get you going.
You can get some group 31s batts that usually run around 1150 cranking amps with a much higher reserve capacity for under a hundred bucks each and the nice part is any truck stop carries the things if one ever goes bad on the road. Truck PRo usually has some good deals on them.