Ok so I have skyline gts25 rb25defactory automatic. I was having ongoing issues with oil getting into the cooling system and after having the head tested skimmed and replacing gasket, issues came back after a month. I since under advice from someone who is the nissan guru here in NZ replaced the block. I decided im not here to root spiders so I sourced a fairly good rb30 block and having an older rb25de (r32 skyline) the head and everything lined up. Now she has been going very good for about a month but every so often it cuts out, like its losing spark and stalling, no backfiring or slow dieing out. It happens at idle, under power, when coasting etc etc. It started off very unintrusively when it was an rb25de it would happen maybe once or twice a week, but recently it seems to happen multiple times in a trip. Apart from a wasted spark setup(and the 30 block) it is pretty much standard in the engine bay. Im sooo sure its electrical but ive checked for loose connections, cleaned the afm and the aac. I can't seem to find anything on uncle google so I was wondering if anyone has had a similar experience and if so how it was remedied. Any help would be appreciated Cheers.

Have you checked the idle air control valve? I was having a stalling problem and cleaning the IACV seemed to help. There are threads around that detail how to do it.