Problem with 89 Spider

[Ciao89@domain.elided]

I've owned my Alfa for about 2 yrs.  I hope I can explain the problem.  It 
only happens on the highway when I'm in 5th gear.  The needle to the battery 
either immediately goes from 12 to 14.  Sometimes there's a sulfur smell.  It 
starts to stall out and some lights come on.  I think it's the one that has 
to do with temperature.  Once I put it in 4th it's better and if I get off 
the highway it stops completely.  It does this every time I get on the 
highway and into 5th gear.  I don't know what's wrong.  Does anybody have any 
suggestions?  I know I'll need to take it in, but it would be nice to know 
why.

Elizabeth A. Arellano

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