Replacing the valve body should solve the problem, but it will eventualy return due to the poor design. The best bet is to use the Trans Go kit.
Trans Go kit can be installed without removing the transmission, so its worth a try.
The more you drive, the more damage is done. If fixed in time, you can prevent damage to the rest of the transmission. Its hard to say how much damage has been done until you install the Trans Go kit.
