I have an 97 PS190 with the LT1 and the power slot. I have always run it on unleaded regular and it is awesome. The only problem I have had was cooling with the factory water bleeds on the low end of the heads. I installed water bleeds on the high end of the heads (very easy to do) and the problem was solved. Recirculating water pumps are expensive for these (factory Corvette). Have 1100 hours with no other problems!
We bought a 02 230VRS and now have the 190 up for sale. We needed more room for our toys. We still love the PS190 but I can't afford two boats!