Should I change fluids in the tranny, rear, power steering and brakes at 85,000

Just follow what the owner's manual says. Ask them to show you where these intervals are written. Alex

Side note: for a 14 year old vehicle, simply staying with the owners guide does not consider the physical inspection and analysis of real world driving. Brake fluid, for example, should be changed every 3 years, and your Chevrolet owners manual likely does not even address it. 3 years is an automotive standard, as brake fluid is hydroscopic -- it attracts moisture, which contaminates it...and in turn contaminates your brake system in time. Power steering fluid does not have any mileage interval, but can be a modest benefit to a power steering system, conditioning system seals and reducing contaminants from the system. Still, it's no emergency most of the time. Transmission fluids typically get replaced on these vehicles for "severe duty" at 50,000 miles, "normal duty" at 100,000 miles. If it's my truck, I'm protecting my investment and following the "severe duty" schedule. The transmission filter should also be serviced. The differential fluid of this vehicle does not have a criteria for changing in the owners guide, but it -- like the power steering fluid - would be a performance improvement / preventive maintenance situation that can't hurt in the long run. Required? No. There is a difference between "required" maintenance and "beneficial" servicing.