It's a 16 Tahoe. In my owner's manual and the brake fluid reservoir cap , they say only use DOT3 brake fluid. I'm wondering if I could use DOT4 or DOT4 Low Viscosity brake fluid?
You can absolutely use DOT4 in place of DOT3 brake fluid. The only thing you'll need to do is completely purge the system of the old DOT3 fluid to take advantage of the DOT4 features (higher boiling point both dry/wet). The only real difference between the two is how hot they can get before they boil. The DOT4 will not harm your DOT3 system in any way. Do not use DOT5 fluid (silicone based fluid), as it is completely different. You can possibly use DOT5.1, which is compatible with DOT3/4. A lot of the different brake fluids you find on the shelves of parts stores will say "DOT3/4" on the bottle, meaning you can use them in either a DOT3 or DOT4 system, but be assured, it will give you the performance of the DOT4 fluid in either.