engine revs , but car doesnt move off that fast, and speed drops considerably on hills.
In seriousness, when there is power to the engine, but it’s not being delivered to the wheels, it would normally indicate the clutch. Often accompanied by a nasty burning smell. Put it in a low gear as you’re cruising, and put your foot down. If the revs rise sharply yet your speed doesn’t, that’s what it will likely be.
I will note however, that my limited experience is with old sheds, rather than new fangled motors made up almost entirely of electrical gubbins.