It is unlikely that the cat is at fault. Warm weather will make some cars slow because the ignition control unit will retard the timing. You can try replacing the temp sensor on the rear of the cyl head.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM