Going down the highway the dash lights flicker and the engine just
shuts down.The alternator was replaced and it does the same thing.It seems
it happens as the car decelerates coming to a stop as if the rpms are too
low.The vehicle has 48000 miles on it.

 

Does your check engine lamp stay illuminated when you restart it?
How frequently does this happen?
When it happens, does the car start back up normally?
Does it stall when in neutral as well as in gear?
What engine do you have?

At present, there's not really enough information to hazard a good guess--
there's just too many possibilities. It could be lack of fuel, an
electrical issue, or something with the fuel management system. More info
(if you can provide it) may help.

I'd recommend returning it to the dealer for service. There's obviously
something wrong.