Problem with Nikon D70s

[King F. Hui]

I am having exposure and focusing problems with my Nikon D70s. I sent it back to Nikon (Richmond, BC) and the only thing they did was to update the firmware. That did improve the exposure a little bit, but the problems still exist. Here are the problems:
1. Using Auto mode, the contrast is too strong and in general too dark (under exposure)
2. Using shutter priority mode, all photos are under exposed, need to use +1.0 to compensate. Also in Shutter Priority mode and taking 5 shots per second, most shots are underexposed and may be one is fine (correct exposure).
3. Using zoom lens at maximum local length, it won't focus (just frozen). It showed a error code "r70" on the LCD panel.
4. Photo grainy when set at ISO400

Anybody has the similar problem? How did you fix the problem? Yeh, send it back to Nikon then I would be without it for 3 weeks.