Dodge ram 50 1987 4x4 2.6

I got a 87 Dodge Ram 50 four by four 2.6
motor been sitting for a few years got it
running replaced fuel filter fuel lines fuel
pump the truck runs like a top but then it will
die after driving a couple miles starts back
up runs like a top dies again it's not with the
fuel I believe it's something electrical what
could it be I was told by a mechanic that
there's a little electrical component strapped
to the coil it gets hot causes it to die what is
this part I was told it's like a condenser or
points more or less