Problems with HTC cell phone?

I have an HTC (with HTC sense) phone... it's great, but I have two problems!

1. Horrible keyboard lag. However, this is just when texting one specific person?! Why? So strange! I actually got my phone replaced, with the exact same model, but I STILL have a terrible lag with the SAME CONTACT. I just don't understand!! It goes away after I leave the phone there with the open message for a few minutes. But it's REALLY annoying.

2. There's a "system error" and it restarts once in a while (tooooo often). Which takes a few minutes. And is super annoying. Randomly. It's especially irritating when I'm in the middle of a long message cuz it doesn't save it.

3. Sometimes, it randomly gets frozen or "crashes". As in, the screen won't turn on after I turn it off or something or it won't respond at all anymore while I'm writing something and I have to re-insert the battery.

Same problems with both phones of the same model I've had! It's so freaking annoying. I'd like to enjoy my phone!! And I just don't understand why, as I don't even have a data plan with internet, no apps at all, not a lot of pictures or videos, no sound or vibration feedback or spell check for text messages that could slow the phone down...

Thank you so much!!