Are you having failure due to No Response, or something else ?
Could you give an exemple of the TBF failure %, hourly, over 24hours ? (the % , but also, the numerator + denominator of the formula)
Please post the UL failure % and the DL failure % separately.
Radio failures should normally be caused by interference :
– try allocating your PDCH on another TRX than the one it is currently using. (the idea is to swap TCH and PDCH, so you can check TCH quality where there were previously the PDCH.)
– ensure your UL GPRS Power Control is disabled. (look for gamma and alpha values) – (Edit : you said you did disable it already.)
– ensure your rx access min is not set too low
– ensure your path balance is … balanced 🙂