We just fixed ours. 2001 500efi, its your thermastat. I bet you have right at 50 hrs on your motor. When it was new it ran 148-152 all the time. Then after a year of use it would slowly go up to 180 and then drop quickly to 140. Put in new thermstat and it stays at 151 now wich is a good temp for the 500efi. When you buy the thermstat make sure you get a new seal also. Inexpensive part like $20 , and one that could really mess up a nice motor.
As for water press I see have the same.