I'm using AES-256 CBC mode in C# to encrypt various amounts of texts. The key and IV are always generated properly randomly. However, would GCM mode provide any noticeable security gains over CBC?
It's a little hard to say without knowing your exact set-up, but CBC may well be fine, especially as it is available in .NET as is.
The main risk of CBC is the padding oracle attack here are some good links:
If you can be confident that an attacker cannot modify the cipher text then you should be alright. You could also go down the route of encrypt-then-MAC to ensure that the actual ciphertext was unaltered.