Or, start by getting a new vacuum modulator. Get the one that's a small gold can and has a RED stripe; not a green stripe, not a pink stripe, not ANY other color but RED; and not the big black can type, either. SMALL GOLD CAN with RED STRIPE. Remember that. It's hard to know what vehicle to look it up for, so just keep looking up for different cars and opening the boxes until you find one with a RED STRIPE. I'd suggest looking up for something like a 71 Chevelle 454 with a Turbo 400, maybe that'll get it but who knows. Be ready to look up lots of different vehicles with Powerglide, 350, or 400; they all use the same modulator. Some will show a listing for some one of the variety or some other; just keep looking them up and looking in the box until you find one with a RED STRIPE.
There's a little screw inside the vacuum fitting. Adjust it inward to make it shift later and harder, outward to make it shift softer and earlier. Move it in ¼ turn increments until you get it where you want it.
Pop quiz: what color stripe should you be looking for?
