Arduino pro mini 3.3V/8MHz

Hello everyone,
I connected Arduino pro mini 5V/16MHz with sparkfun silvermate (Bluetooth) and can transfer data without any issue. However, if I use 3.3V/8MHz (ATmega328). I can not communicate bluetooth. Basically bluetooth read giberish.
I also tested increasing pro mini's voltage with 3.8V. I found Tx pin of bluetooth increases at same level. However, Rx pin stays at 3.27V. I am not sure this is the reason.

I am simply trying to find a solution here. If any one can help me that will be great.

WHat does the Sparkfun module expect?

+5v or +3.3v?

Did you add a level/logic shifter in your +5v approach?

Did you remove it in the second approach/try?

I'm not familiar with the: silvermate (Bluetooth) module.. but for regular old HC-05 BT modules..

I know you had to (at least) have a voltage divider to get the comm lines down to +3.3v for it to communicate correctly.

Also.. same serial/baud rate set on each approach?

Links to you BT module and some posted specs might help other identify whats going on.