strykeroz:
Like billroy, I'm only speculating but I'm not sure VCC versus clock speed will be it. My power source of choice for ATTiny85 projects is a single CR2032 and I've never had an issue with them operating at 8MHz (I always burn that speed too). Though to be fair, I'm not doing serial comms in anything I'm referring to here.Perhaps it's worth consulting the data sheet to see also what voltage the ATTiny is producing for a HIGH signal at 3V. You might just find you've gone below where the Uno reads a HIGH, so your serial comms have become a stream of zeroes to the receiving side.
Cheers ! Geoff
I have no problems running the chip, it really only has to do with serial output. I've gotten it to even output "PWN" (software on a few pins) on 5 pins, so it seems like it's pushing it hard. But I will check out the datasheet, I didn't think to check if it's outputting enough power for HIGH on arduino.