If your HD running fine in WM6.1, the chances of hardware issue is slim. You should ask your friend to flash the ROM again and hard reset twice after
flashing.

Dont install any 3rd party apps and play around with it. If it is still unstable, then flash back to wm6.1 original and send to SIS.

In my opinion, WM6.1 is faster and smoother than wm6.5 not to mention battery life is better. I have flashed so many rom (Davideuck, Dutty, Miri and kwbr)
and personal opinion, prefer wm6.1

Currently I'm using kwbr Topix HD Unleashed 3.0 (manila 2.1, hate manila 2.5, again personal opinion).

Cheers,

Danny

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Added on October 4, 2009, 5:59 pm
I'm using radio 1.17.25.09 more than 2 weeks. My battery life is ok, in fact I feel it's better. Moderate use (30 minutes call 3-4 times a day and more than 10 calls lasted around 5 minutes) can last me two days easily.

I switched from wm6.5 back to wm6.1 and boy, i dont have to charge my HTC HD daily. Currently I'm using kwbr Topix HD Unleashed 3.0 (wm6.1, manila 2.1).
Cheers,

Danny