My speedometer is OK until about 45, but if I go faster, the needle doesn't go back down until I slow down to about 35, and then it drops. Would this be the speedometer itself, the cable, or something else?

I would say it's the speedometer itself.

Most likely, it's has some transmission lube in it, which causes them to do weird things.

 

There is an o-ring that seals the speedometer drive on the trans. It can let the lube wick up the cable and get into the speedometer.

 

My White '86 BRAT had that issue. Quite a lot of trans lube at the dash connection, and surrounding area.

What a mess...

 

Uncertain of actual repair for it.

But you can pull the cluster out and clean the speedometer with some carb cleaner.

can  you small gear lube ?  dead giveaway

i'd guess that its the cable itself.

 

either get a new one,

or lube the cable you currently have.

Sticking needle would be in the meter. Most I have had developed the sticky you describe. I "fixed" it by using my gps For speed. The speedometer cable is just spinning, no directly connected to the needle. There is a viscous coupling that works against a spring to translate the rotation speed into the movement of the needle.