I think it might be a B movie from the 80s.

What movie is it where a guy and his wife get stranded by the road then separated and his wife goes to hell or some other dimension and the guy loses his arm and gets a gun or chainsaw implant?

what movie is it where a guy and his wife get stranded by the road then separated and his wife goes to hell or some other dimension and the guy loses his arm and gets a gun or chainsaw implant?

This part sounds like you're describing Ash from

The Evil Dead II

But the young couple's stranded in an isolated
Cabin in the middle of a haunted forest, not stalled
At the side of the road.
Ash's hand's possessed and he must amputate it.
He finds what he needs to fight back in the toolshed.
Ash attaches a chainsaw to the end of his arm, and
Carries a sawed off shotgun in his other hand

view (http://www.youtube.com/watch?v=IGyCXvzmdYc)

The first part sounds like Highway to Hell (http://www.imdb.com/title/tt0104418/plotsummary)

It's either Evil Dead 2 or Army of Darkness. One of the two's got the same actor in it.