The Z-Trak mowers usually take a different blade than the MMM do for some stupid reason. To the best of my knowledge, there are no high lifts for the 54" deck like the ones under the GX series like there were for your old 38" deck. The ones that come under your 54" are basically medium lift blades, but they work pretty well IME. I don't know if you're old school or not, but many old school guys don't run their machine at WOT. You should for several reasons, including cooling, efficiency of the implements that go with the machine etc.