there is a thread in here on how to get high boost setting through out the rev rang, pls search
go here http://www.skylinesaustralia.com/forums/in...showtopic=42895
check for water in the oil , and compressing test the raidator if you are worryed about it being a head gasket, sorry to say if you cant find it your self, take and pay someone to fix it. Use a specialised raditor place or good machnic