some info below from a quick google search. Hope it helps or is there something specifif you're after.
READQ TS - INVREQ NOT QIDERR
CICS TS will now return an INVREQ for an EXEC CICS READQ TS QUEUE('queue') - where 'queue' is low-values. CICS Version 4 returned QIDERR. Some application programs test for QIDERR to identify that the variable 'queue' has not been set yet. Application logic needs to be changed or the Global User Exit, XTSEREQC, could be used to set EIBRESP to QIDERR and emulate the CICS Version 4 response.
DEFAULT CICS WEB INTERFACE USERID
The CICS Version 4 Web interface facility provided a configuration transaction (CWBC) that allowed a default Web user-id to be specified. The CICS TS Web interface configuration is done using CEDA and a default Web user-id is not part of the new RDO definitions.
To set a default Web user-id with CICS TS 1.3, it must now be set in the Analyser by checking and setting COMMAREA field WBRA_USERID.
EXEC CICS START WITH REQID - IOERR
EXEC CICS START FROM(xxxx...) REQID(xxxx...) no longer operates like it used to under CICS 4. The response of IOERR can now be given when a duplicate REQID is used - this was not checked under CICS/ESA 4 (although the results would be unpredictable if a duplicate REQID already existed).
NEW CONDITIONS: LOCKED AND RECORDBUSY
Even without making use of RLS, the new conditions (locked and recordbusy) can be seen when accessing recoverable resources in CICS TS. Code that accesses recoverable resources needs to be reviewed in the light of these new conditions possibly being received. Check the CICS Recovery and Restart Guide for more details.
EIBRCODE AFTER ILLOGIC RESPONSE
Bytes 3 and 4 of EIBRCODE now contain VSAM return codes rather than NULLs. This can be helpful, but code comparing the EIBRCODE with user-defined constants needs to be reviewed.
The CVDAs for EXEC CICS INQUIRE TERMINAL requests are no longer made available in certain cases. For example, under CICS/ESA 4, an EXEC CICS INQUIRE TERMINAL for CREATESESS issued against a surrogate terminal would return a 67 (CREATE). Under CICS TS, a CVDA of 1 (NOTAPPLIC) is returned. This is apparently an intentional change to make the code match what the manual states.