25% TCA Peel Vs 35%?

I am not surprised that you got little results with your 25% peel. Unless you do many of them, this is often the case. A 35% peel may indeed give you the results you want, depending strongly on how it is applied.
In general, the deeper the peel, the stronger the results are. However, the risks—including risk of hyperpigmentation (to much pigment) or hypopigmentation (skin whitening)—also increase along with it. Also, the recovery period is longer with a stronger peel.
Nonetheless, with a stronger peel, the top layers of the skin are destroyed (hence the darkening and then peeling off of the skin) more effectively. When the top layers are destroyed, the body is forced to regrow or regenerate fresh new upper layers of skin, collagen and elastin that give the skin a younger, smoother, less-wrinkled, and more even-pigmented appearance. Given the fact that you have told me that you have light skin (post-peel pigment problems are less common with light skin), I would agree that you consider a stronger peel to get the results you want.

It is difficult to tell whether the "hyperpigmentation due to sun exposure" you are describing might be melasma (hormone-related pigmentation) or lentigos (sun spots).
There are in general, two forms of melasma: superficial and deep. The more superficial melasma is more accessible to chemical peeling agents, whereas the deep pigment is not. Some improvement in your brown spots is still encouraging.
The pigment may resolve to your satisfaction with additional TCA 25% peels. For pigmentation only, I would stick with the 25% since there is more risk of complications including pigmentary problems with 35% TCA.
You might also consider some laser technologies, e.g. Fraxel that can penetrate somewhat deeper if you indeed have melasma.
Good luck.