Airbox modded XR5 overheating ECU issue?

[sotheby]

Hey guys and gals.
I've an MA XR5 that I modified by July of 2008. It's been fine until recently. : The car currently has the following:

1. Bluefin ECU code. 196kW and about 409nM torque.
2. German ECU module spacer kit. ECU cover removed.
3. Pipercross triple ply foam [washable] airfilter replacing the paper element.
4. Unrelated German Ford aluminium pedals, fitted by Ford Australia.

Issue: The car has 'survived' the last hot summer without problems. For the past month it's been stalling when:

stuck in 1st for long periods of time with the
air-conditioner active

Generally this means Christmas queues at shopping centres, and a few days ago when stuck in traffic queues returning from Brisbane at good old Ballina. I washed the air filter about a month ago, and it was pretty clean anyway. My gut feel tells me the ECU is overheating because the heatsink fins are no longer in the airbox feed airway. Once the car is under way - 3rd gear upwards, the stalling problem disappears. I'm thinking of adding some "super heavy duty" Jaycar heatsinks to the smooth front-end facing plate of the ECU housing for additional heat dissipation.

Any ideas folks? Thanks in advance!