Flush Transmission and Radiator?

At 60 k miles I would change it. You don't know if the transmission was ever overheated when climbing long grades. I change mine every 30k miles or so. You would be surprised at the debris in the bottom of the pan on the first fluid change. Each subsequent change showed less debris. I change the fluid in the rear end every 30k miles also. I don't know what your MH weighs but the heavier it is the more load is on the transmission especially climbing hills. After you drop the pan and change the filter look at the magnet on the bottom of pan and clean it off of metallic chips. You can disconnect the transmission line to you radiator and run all the old fluid out buy running your engine and adding new fluid until all the old fluid is flush out. This will get the old fluid out of the torque converter unless you have a drain plug in it.