A faulty fuel pump would cause your Navigator to hesitate when you accelerate. Bad gasoline could also be at fault.
Change the fuel filter and have the cat convertor checked out
Sounds like it could be a dirty fuel filter, try taking it off and cleaning it.
Because you bought the 1.6. Get a 2.0D and the problem will go away.
A leak in the brake booster is one common reason why a car would stall or hesitate when the brakes are pushed. There could also be an obstruction in the brake line.
Timing chain - sloppy?
low trans fluid level.
There must be a restriction within the intake. Snow? ice? Mark
A car goes faster when you accelerate. It slows down when you brake.
I don't have a car.