Exhaust smell in cab

Exhaust doesn't come from under the hood if there isn't an exhaust leak, but gas smell could.
If it is actually exhaust and everything back there is sealed up and any holes are plugged you may very well want to move the outlet to a different place.
A moving car creates a vacuum behind it and if the exhaust is in that vacuum area it can suck it in through a bad trunk seal, missing body plugs or any other open spot in the rear of the car.

Of course it could be running rich as hell also, and that'll do it.