You could also use spacing for that.

>>>
>>>
>>>

^ Steep hill

>   >   >
>   >   >
>   >   >

^Gradual incline/decline

Something like this for all of them?
(decline right, decline up, decline left, decline down)
Gradual:
>  >  >  ^ ^ ^ <  <  < v v v
>  >  >  ^ ^ ^ <  <  < v v v
>  >  >  ^ ^ ^ <  <  < v v v

Moderate:
> > > > ^ ^^ ^ < < < < v vv v
> > > > ^ ^^ ^ < < < < v vv v
> > > > ^ ^^ ^ < < < < v vv v
Steep:
>>>>> ^^^^^ <<<<< vvvvv
>>>>> ^^^^^ <<<<< vvvvv
>>>>> ^^^^^ <<<<< vvvvv


Was grounded for a few days from the computer

But anyways, so far I haven't really worked on the engine yet   I was working on another game I might post about if it ever gets anywhere.  I also like the idea of the closer the arrows are, the steeper the incline is.  Today is going to be an unproductive day I can tell, so I'll probably end up working on this at school tomorrow.

I wonder if isometric maps would be fast enough. Something like Kirby's Dream Course

They would be fast, but believe me, isometric is tricky when it comes to making a map from tiles.  And, an isometric tileset requires more graphical data.  I'd say an isometric map requires about 50% more tile data than a regular map

Couldn't you divide the tiles in two and have half-tiles? Or would that just murder speed?