I had 1978 messages, to be exact, and was having those issues. The messages were restored via MyPhone, re-threading of the messages was pretty quick.

As soon as I cleared my message database, the messaging app immediately acted right. Still, my phone started randomly running out of memory the next night, and wouldn't open apps (and wouldn't accept new text messages). So I had to hard reset.

I haven't restored my text messages and haven't been having any issues.