Why does my Ford Focus shake when maintaining 70 mph?

I've got a 2007 Ford Focus hatchback. My husband did an oil change on it about month ago. Since then there's a vibration. Everything feels fine until you go 70 mph. While trying to maintain the speed the whole car shakes. It feels like it is about to stall, but doesn't or at least, hasn't yet. The shaking stops when accelerating or decelerating. Its an automatic and the engine light pops on and off. It only happens while trying to maintain speed in the 69-71mph range.

Sounds like wheel balance, get your front wheels balanced any tyre place will do it.

Ford focus tends to be unstable at high speeds.