Re: John Deere GT262 Drive Belt Issue
There should be three pullies on the drive belt; one at the crankshaft, one at the tranny, and a spring -loaded idler somewhere in between that maintains tension on the belt. Make sure the spring has a good bit of tension on it, sometimes they will get weak from rust, heat, or just age.
It's definitely a loose belt issue, either not enough tension or worn-out belt. The tranny puts enough load on it in the higher gears that it begins to slip. Do you ever smell burning rubber?. The pin that retains the belt on the trans pulley may be bent out or worn from friction with the belt. It also is bolted to the frame or tranny to permit removal for belt changes, it may have come loose.
Check the pulleys for wear. If the belt has been slipping for a long time, it will increase the wear on the pulley. The pulley may need replacement from being worn out, and even a new belt won't stay on.