Every time this question comes up, some are quick to say they have tried it in their motors w/o any issues. But, lubrication issues seldom pop up until considerable run time has occurred under typical wear scenarios or under stressful scenarios.
I dunno 'bout Uz, but I can't afford to experiment with my engine - too rich for my not-so-deep pockets. Therefore, I would prefer to see some comprehensive, scientific testing and comparisons between historic results with a former recommendation lubricants and the new product (good as it may be!).
Our LT5s are flat tappet motors and rev limits are ~ 7100 rpm to 7500 rpm (in some modifications). And, the ZDDP of the oils recommended at the time they were being built (by Mercury Marine), the zinc/phosphorous levels were in the ~1200/1300 ppm - to accommodate the demands of those (LT5) engines.
However, air pollution mandates resulted in reducing (in part) the ZDDP levels. And, offsetting the reduction of reducing the ZDDP, flat tappets gave way to roller tappets and rocker arms, etc.; both roller tappets and rockers are still in use today. My point is:
aren't we comparing apples to oranges here? That isn't to say that this or that GM oil recommendation will spell trouble for our first gen LT5s. But, it remains to be seen if the new oil recommendation can bridge the gap between the specific application (roller tappets/lower rpm vs. flat tappets/high rpm) requirements.
Your mileage may vary. But, as for me - I'll stay with the "Kool-aid" until something else proves to be better...hopefully in an application other than MY LT5! Just sayin'
