That should rule out the memory being faulty and since it freezes while gaming I'd say it points to the GPU, have you got access to a spare GPU to test?
I do have another RX480 (4GB version) would be a bit of a bugger to change them as my 8GB version has a full cover waterblock on it.
However, considering the cpu just broke doing the exact same thing the replacement is doing, is it not more likely to be the PSU or even the motherboard?