Doeasn't address your issue and Wiz has already done that but AFAIK, no utility is capable of reporting actual VRAM memory usage, what they do is report memory allocation. Knowing the allocation is a good piece of data; it's just that most folks don't realize that there's a difference. As long as you don't assume that because GPUz reads 4.5 GB on an 8 GB card, that 4 GB is somehow NG, you're fine. Switch to a 4 GB card on the same system / settings / resolution and you will see a lower reading.
The best analogy I have heard is akin to a credit card. You have a $5,000 credit limit and $2,000 charged on your credid card. You then files for a car loan and when the bank runs acredit check, it sees $5,000 as a liability not $2,000 because you may only have spent $2k, but you have been "allocated" $5k.
Here's a technical explanation, perhaps Wizard can give a better one.....
Such Utilities do not "actually report how much VRAM the GPU is actually using — instead, it reports the amount of VRAM that a game has requested. We spoke to Nvidia’s Brandon Bell on this topic, who told us the following: “None of the GPU tools on the market report memory usage correctly, whether it’s GPU-Z, Afterburner, Precision, etc. They all report the amount of memory requested by the GPU, not the actual memory usage. Cards will larger memory will request more memory, but that doesn’t mean that they actually use it. They simply request it because the memory is available.”
You can see this in dozens of examples using cards offered in two VRAM configurations. Whether the 770, 960, 1060 testing shows many instances with the larger version of the card reports using an amount greater than the smaller version has. And yet when you switch cards, the numbers change ... there's also no significant difference between the fps, image quality between the two cards. Yes, if you go to a big enough resolution (2160p) and the highest possible settings you will see a difference between the cards in the more demanding games. But when you do this, the game is unplayable in either case. Yes the card with the larger VRAM might deliver a 44% improvement in fps, but when that improvement is from 13 fps to 19 fps, the game is still unplayabale regardless of VRAM on baord. I have seen some exceptions, like poor console ports and I have seen the youtube videos where peeps have **created** an issue with significant effort (was a popular past time with the 970) but test sites were never able to duplicate these problems under "normal usage".