TCP tries really hard to avoid fragmentation, by setting the DF flag and reducing the MSS when it sees a PTB error.
Of course that sometimes fails, so if you still have TCP fragmented segments, the next best thing is to filter by source/destination address, saving to a PCAP file, then run tshark on that file with the "-2" flag which does packet reassembly.
(I don't know if tshark can be made to do on-the-fly reassembly, that would require keeping a buffer of un-reassembled fragments until the rest of the packets are seen.)
Of course that sometimes fails, so if you still have TCP fragmented segments, the next best thing is to filter by source/destination address, saving to a PCAP file, then run tshark on that file with the "-2" flag which does packet reassembly.
(I don't know if tshark can be made to do on-the-fly reassembly, that would require keeping a buffer of un-reassembled fragments until the rest of the packets are seen.)