Kristall-99

So i recently bought a FD from a guy in Chicago. I trailer'ed it back to Omaha and began work till summer rolls around there seemed to be a lot of DIY shortcuts made so im in the process of fixing those as well as replacing all the common fluids, coolant and oil. The cooland went well, drained coolant came to be a dark yellow/green tint and washed out, refilled with new coolant and was good to go. I tried to find a good thread that wasn't a what oil to use thread and always heard royal purple was what people recommended. Meanwhile as i was finding a store that carried this I asked the previous owner what oil he used. He responded with regular 10w30. I drained the car and oil radiator and began to fill. As I took her out today for a quick whip around the block i noticed my oil pressure gauge kept fluctuating. Could this be because of the new oil? Did i do more harm than good from going from a standard 10w30 to a more pricier and different weight of oil?

Thanks
Bryan.