Tiagra upshifting jumping 3-4 gears in middle of cassette
That sounds like the shifter itself is malfunctioning.

If the cable or derailleur was hanging up you would get delayed multiple upshifts after clicking the lever several times, but you are saying that a single click results in a 3 sprocket upshift. 

My guess is that the pawl mechanism in the shifter has worn and is slipping when upshifting, but is managing to hang on when downshifting. To confirm this you could try detaching the shift cable from the derailleur, putting tension on the cable manually (as close the shifter as possible if you have exposed shift cables, to eliminate cable or housing problems from the test) and seeing if you can get the shifter to slip when upshifting. 

If the shifter is the problem, they are not serviceable. A replacement is necessary.