I sent my TPT in for repairs for the same issue. They need to replace the circuit board. Initial turn around time was 5 business days. I said "ok". Now the estimated wait time for the part is 3 months.
I regret my purchase and I don't think I will buy another lenovo product based on my experiences with their service dept.
Sigh... another bizarre Lenovo Tablet bug... I've been having the same 'sleep of death' problem (tablet shuts down some time while asleep) but may have found a solution. I set the WiFi to turn off when the display is off, and haven't had the sleep of death problem since. I used to have it nearly every day. Of course, as a user, I'm at a loss why I had to screw aroud with my tablet for days to figure this out. Don't get me started about Lenovo 'service'.
Anyway, here's how to get to the setting in case you want to try it:
Wireless & networks > WiFi settings > (Menu) Advanced > Wireless Enhanced Settings > Turn off Wi-Fi when display is off
I set mine turn off the WiFi 10 minutes after the screen shuts off.
Now for a rant. Lenovo should be ashamed of the mess they've made of this tablet. They should either commit to the thing or get out of the tablet market. So many crashes, little annoying bugs, weird pop-ups that make no sense... I'm no Apple fan but, seriously, that's a company that understands the whole product!
If the Thinkpad Tablet product manager is reading this, could you explain what the plan is to make this a solid, competitive product?