Depends on how old or worn out they are, my G5 was a tad slow until I gave it an oiling in a few places, and my G3's transmission was loud and jerky until, you guessed it, I greased it (well, greased the flat roller bearings, oiled the bronze sleeve bearings), and that quietened it down and stopped it being jerky...
So, like any transmission, lube it if it's not working right, bearings will only last so long when bone dry, and inside of a Kirby techdrive can get pretty dirty with the clutch plate material getting everywhere, so they do need servicing every now and then, you just have to ignore the "breaking this seal will void the warranty" sticker, and have a modicum of bravery....
Not to mention, under the power switch pedal, there's an adjuster nut, fiddle with that and you can get it to work a bit faster going forwards or backwards (depending on how you adjust it), and of course adjusting the slide bracket on the top where the handle connects...
