1999 Chevy Suburban fluid turned brown

Any signs of fluid contaminated by petroleum products, such as swollen master cylinder lid rubber gasket? You probably need to do a complete flush of the brake fluid and start from there. Start with the contamination question and we can go from there. If the fluid is contaminated with a petroleum product, motor oil, trans fluid, etc, you are facing a big expense. Has someone else recently serviced the brakes or added fluid?

No one has serviced my brakes last spring I had the brake system bled and refilled and the the fluid turned brown again I do tow a camper with the truck but it has its own brakes front and rear brakes are in good shape what should I do?

If there is no sign of swollen rubber components I think I would do a complete brake fluid flush and refill with fresh GM DOT 3 brake fluid which is clear in color and then re-evaluate any problem which may still exist.