If your cake is dry, it could be that your mixture is to stiff, add a little cool boiled water, the mixture should look like stiff whipped cream, you could be over cooking it, 25 mins on 180 is about right, and remember it will continue to cook for a few minutes when you take it out of the oven.
When you say on the diagonal, do you mean it rise more one side than the other, if so the. I would say your oven isn’t heating evenly, the door seal could need replacing.
If your cake is browning on the top to much, but a baking sheet on the shelf about, this will protect it a little. A fruit cake benefits from a dish of water in the bottom of the oven to create steam, and always line your pans.
Giving away all my trade secrets now !