merc sprintshift problem

My sprintshift slips from Auto to manual mode from time to time, seemingly when the weather is very hot.

Switching off and back on again has, so far, solved the problem but that's not always easy to do.

I noticed, yesterday, that the turbo is not working either under these conditions and using manual shift.

It seems, to me, to be due to something electrical overheating. Has anyone else experienced this?

Merc 414 with 40,000miles