The cheapest route, and probably what I would do until you get a better solution figured out would be to shim the battery post with some pieces of metal. You can probably find some thin metal lying around that you could cut to use for that purpose.
I dont know anything about optima batteries, but I would think they would have side post connections too, where you could screw in a battery post into the side. If you used those instead of the top posts, the cables might reach better.
Was this battery new or used? If it was used maybe the previous owner filed the crap out of the terminals to clean them, making them smaller? If that is the case, the terminals may screw out and you could probably order a new set from optima, or your local parts store may carry battery posts.
If the battery was new, you should be able to get a new battery connection terminal for your cable from an auto parts store or a car audio shop. Keep in mind you are going to have to crimp it and crimp it good if get one. Very tricky to do it right on the truck.
You can get a length of wire from any car audio shop to replace yours if it needs to be that much longer. However, a lot of times, manufacturers use clips to hold wires taught and out of the way. Follow the battery wire back as far as you can, and see if it has any clips holding it to the fender or something... popping one of those off might give you a bit of extra length.
These are all ideas, I dont know a thing about optima batteries.
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