An iPad will only have a sim card if its cellular model. sim cards are used to connect to cellular service.
Its very unlikely it would solve any instability issues.
Perhaps if you explain what exactly its happening or how it is unstable, and why you do not trust it anymore, someone may be able to help.
In the meantime you can try some general troubleshooting steps:
- A Reset may cure some bugs. Hold down the Home and sleep/power buttons until the apple logo shows up.
If still not resolved:
- Reste al Settings. Go to Settings->General->Reset->Reset All Settings
If its still not resolved:
- Restore the device: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
If still not resolved:
- Restore the device as new: Restore your iPhone, iPad, or iPod to factory settings - Apple Support