farrow resampler in timing recovery

My receiver contains: AGC,timing recovery,carrier recovey blocks.

I am using gardner timing recovery with loop filter and farrow parabolic filter.
The input to the farrow filter is the fractional delay. I am assuming the fractional delay should be constant after preamble time may be only small variations. The fractional delay does not settle in the preamble time.
Between two data burst only pure carrier is sent so there any no transition for
timing recovery to work. So immediately after the data burst there is lot of variations in the frac. delay. which causes timing errors. any suggestions???