So, how do you get the car to manually shift into fourth from third?

 

3 to D ?

 

Yep... staying in 3 will stay in 3rd gear (perfect for around town).

 

For shifts down to 2 at medium speeds (that can seem a bit harsh if there's a biggish rev difference) I find it helps if you give it a bit of throttle as you move the shifter - you get a smoother kickdown-type downshift rather than an engine brake/under-rotation type of shift, if that makes sense!

Presume it's helping to rev-match a bit better and is sympathetic, not harmful to, the transmission?