"yes it's a mismatch. 190
"yes it's a mismatch. 190 was behind a 302.
But that has nothing much to do with your symptom.
The jumping out of gear may be due to the water in the lower. Water conducts electricity and can therefore short out the clutch coils in the lower unit. The special "type C" oil that you used in your lower is a high resistance oil to prevent that, but when water gets in it can disengage.
btw, you don't actually need to use that $pecial oil in your upper, or intermediate.... just the lower where the electric coils are.
More common is a broken clutch spring tang or tab. You'll see when you take the lower apart.
When you disassemble your upper, you can count the teeth in there and compare to the link I posted above to see if you have 190HP gearing or 235HP gearing.
Either way, if you have the right propeller, a 190 may work ok behind your 235 hp motor.
Gear ratio and prop pitch factor together to provide the correct WOT engine rpm."