Your LN3 has alot of miles on it.
The passages in the trans core of the radiator are VERY small.
We currently have a car that is killing a REBUILT trans because the rebuilder failed to bypass it.
I'm a firm believer (from experience) that the trans must be protected, particularly from a boost setup that produces more heat, and even more particularly in a high-mileage trans or a rebuild after the first trans failure, and even MORE so when you're putting an inferior trans under increased stress due to supercharging, as in your case.
Test me. Cut a junker radiator apart, and cut the trans 'core' which is really only about 6" long in half and look at how small the passages are for fluid to flow through. It'll scare the **** out of you, and you'll go take care of it really quickly.
The same applies to cooling the oil. It was done on L67'* by the factory for a reason.