If you don't see an appreciable difference in PTO load with the standard high lift blades... you have bigger problems (spindles, PTO bushings/alignment, U-joint wear, etc.).
It's worth noting... if you have the Guardian Recycler mulching deck (pardon me for not scrolling back to verify), you will always have problems when cutting more than 2 or 3 inches of growth. They simply can't process the clippings into small enough pieces to fall out of the vacuum, through the blade path, and back to the ground. Mulching decks process clippings 3 to 8 times as much as side or rear discharge. Furthermore, unlike other decks which will force evacuate clumps... mulching decks simply load up in the top of the blade chambers, increasing turbulence and load on the blades.