Adjusting the throttle valve cable will change all the shifts except torque converter lock up. A tighter T.V. cable will shift at higher mile per hour points plus harsher and earlier downshifts. A looser TV cable does the opposite. A small adjustment on the TV cable makes a lot of difference. Be sure to mark your starting point with a wrap of tape around the cable. I believe the 2-3 shift point can be spaced closer to the 1-2 shift point by changing springs in the valve body, but you'll need a tranny guru, which I am not.
The adjustment screw on the side of the valve body will move both the 1-2 and the 2-3 shift points at the same time, not independently. This is really where you should do the adjusting and not with the T.V. cable.
If you're wanting firmer shifts more pressure and larger holes in the valve body plate can accomplish this.
Might need to contact Tim Holt or Dave Goerend, they are real guru's