Portra 800 developing etc?

[candyspan]

Hi everyone, please forgive me if this topic has been cover, but I wanted to know anyone's experience with 220 Portra iso 800. I'm having a hard time developing it, it's either severely underdeveloped, or over, and there is a TON of grain. Maybe it's my exposure, but I don't think so since I'm not having any other problems with my other film. I'm developing it with either Arista color developing kit from Freestyle photo, or I get one of the Unicolor press kits if I'm out of anything else.

Any general suggestions or specifics are greatly appreciated. I shoot with a Mamiya 7.

Thanks in advance!

D