The game has lots of issues for me, it often becomes unresponsive at the traderscreen, I still can move the mouse but not click on anything,forcing me to ALT-Tab and quit.
Sometimes when I try to leave a town, the screen goes black and nothing happens anymore or it goes black and dosbox quits.
Then also sometimes, the game becomes very laggy, sound stuttering, mouse moving at 1FPS, again forcing me to quit the game.

Qbviously the game is unplayable like this.

All I changed in the dosbox ini file was switching from overlay to opengl, apart from that the ini is unchanged. Switching back to overlay doesn't help either.

yes switch & run it in open GLwindowed mode.


see here my good man- from gog pirates! gold support article(s)

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Launching or stability issues
PLEASE FOLLOW BASIC TROUBLESHOOTING STEPS:
- Please make sure that you use "Run as Administrator" to install and to start the game (right-click on the shortcut or setup file and select "Run as Administrator").
Please note: This doesn’t apply if you are running the game via GOG Galaxy.

- Please update your graphics device drivers:
https://downloadcenter.intel.com/
http://www.nvidia.com/Download/index.aspx
http://support.amd.com/en-us/download

RUN THE GAME IN OPENGL AND WINDOWED MODE
Please go to the game installation folder:
- If the game was installed via Galaxy, please select the game in GOG Galaxy, click on More -> Other -> Graphics Mode Setup
- If the game was installed via offline installer, then you will have to manually navigate to the game installation folder, by default it's:
C:\GOG Games\game-title\
Once in there find and run Dosbox Configurator.
In Graphics Mode Setup tool please select:
Graphics Mode: OpenGL
Fullscreen: Unchecked
Go to Advanced Options.
Windowed Mode: Select 1280x720 or resolution closer to your display resolution.
Press Save and close. Now try to run the game.



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Screen freezes after launch (Intel HD graphics issue)
IF YOUR COMPUTER IS EQUIPPED WITH A DEDICATED (MORE POWERFUL) NVIDIA OR ATI/AMD GRAPHICS DEVICE
You should perform the steps below to use the superior card.
For an NVIDIA card, go to NVIDIA Control Panel -> Manage 3D settings. You should be able to select the NVIDIA card as the preferred device or create a profile for the game to use it.
For an ATI/AMD card, go to Catalyst Control Center -> Power -> Switchable graphics. You should be able to select High Performance for the game - this should make it use the Radeon card.


IF YOUR COMPUTER IS ONLY EQUIPPED WITH THE INTEL HD DEVICE
Try to start the game with a second display attached or follow this tutorial to create a virtual one:
http://files.gog.com/support/tutorialcopy.jpg