Uplink TBF is uplink temporaly block flow. It is GPRS related. Here is an explanation “Unidirectional flow of data between MS and PCU for the transfer of one or more LLC PDUs”.
Also several TBF can be transmitted on one PDCH. Also one TBF can be served on several PDCH.
About SDDCH drop what kind of equipment do you use? There should be counters for different reasons for SDCCH drops e.g. T200 expire, Radiolink failure etc. Check which one do you have.