Loss of speed when turning

Novice back for advise! I have had 2001 Outback for the past three years. During the past month, when we make moderate to tight turns, we lose much more speed than usual.
- RPMs drop off a little.
-Increasing throttle in the turn does not help.
-Performance is fine when running straight.
-The prop does not have any damage and does not seem to be loose.
-Only dumb thing I did lately was leave the gas cap off when running the both for about 30 minutes.

Suggestions? Well, other than making sure the gas cap is on.....

It all depends on your speed also, when you turn you create a lot more drag on the boat and this is the initial reason for it to slow down. If your not running weight and in moderate turn you cant maintain speed with additional throttle then you might look at your fuel filter, look at your carb settings, and ensure that you have full throttle operation at the carb when you move the throttle to WOT.

Depending on your prop, you might be cavitating through turns due to the extra drag and the prop cant maintain speed.