You are trying to achieve what is called passing gear at WOT. You need to install a part throttle kick down valve on the valve body . Easy to do just three screws. Also take the governor piston out and install a lighter one with a stronger spring from a 340 or max wedge trans. This will make the trans hold the shifts longer .
340 or max wedge governor on right. With a lathe you can make one , A&A sells them
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