These steps can be helpful for migration scenario:
1. Do static check on your code using ATC (in Dev system)
2. Do dynamic check on code using SQLM (If available) (in PRD)
3. Use SWLT for creating priority worklist and identify code which can be optimized by merging result of Static and Dynamic check results
4. Use ABAP profiler(eclipse) or SAT to better understand the issue for each item from SWLT
5. If issue is related to SQL, ST05 can be used
Thanks,
Sumit