When your stash starts to accumulate multiple items, their tabs starts to overlap each other, making it difficult to see which is which and difficult to select which is which. I propose a simple solution where you the item boxes be shrunk by 25%. In order to maximize the image space, the items should be displayed diagonally inside the squares for big items such as guns.
The image should still be reasonably small enough to still be discerned without difficulty. When you move your cursor to on an item, it automatically enlarges, to prevent overlap, the items by the sides will be "pushed" to the side.
This is my simple proposal for an overhauled stash display.