Sticky tires, I see,.....
A tight LSD, grippy tires, and wheels off and back on the ground under full throttle is a recipe for transmission failure. Those kinds of shock loads are difficult to guard against besides making certain that the rear suspension has sufficient droop travel to ensure the tires remain on the ground during elevation changes.
If the driver keeps his/her foot more or less planted on the throttle when the car settles back after a bump or over a steep rise, this sort of thing will happen and its very difficult to prevent without lifting a bit. Suspension changes may be necessary.
If your rear suspension is working properly: proper rebound values and sufficient droop, then you may consider replacing the 915 with a G50. This is after all, the main reason why Porsche eventually replaced the 915 in the 3.2 litre cars.
I'd suggest reviewing your suspension setup, as above as well as feathering the throttle when the car's suspension is really unloaded.