Brad,
There are GT's within range of Gladstone. I fish out of Yeppoon and if we head south we meet Gladstone boats heading north.
There is a lot of fishing pressure around Gladstone, but I have never seen anyone fishing for GT's.
So far all I have done is fish the obvious spots and done pretty well. Send me a pm closer to the dates and I'll give you a couple of good starters. There is a bit of a pattern up here that the Spanish Mackerel haunts also hold GT's, ie current, rock ridges, bait schools. You should be able to get good intel on Mackerel then work the spots for Gt's. I haven't seen many Gts around the offshore reefs and shoals, they tend to be a bit featureless. I would concentrate on the continental Islands and mainland headlands.