I would also recommend the built-in WSPR function in KD8CECs firmware to calibrate the frequency offset.
Calculate where you should send, then check your reports on wsprnet.org and calculate the average deviation.
Then you can calculate the new calibration value according to the formula on KD8CECs homepage.and upload
it to the raduino.
The BFO adjustments are really a bit hard - I would start with a value which is working onsomeone else's uBITX.
In your case it should be a V5 of course.
My new V5 was nearly deaf on CWL and CWU - then I found a value in this group from someone who had had the same problem.
Worked like a charm.