Loosening, or adding slack to the TV cable will make it shift sooner. The proper way to adjust the cable is by installing a pressure gauge on the port on the side of the tranny, and adjusting cable to, I believe, 35psi. I'd recommend a professional and trusted (if there is such a thing) transmission shop do this. I run a LenTech Street Terminator Lock-Up valve body, and adjusting it as per the directions, made my tranny shift too late. I simply "loosened" it, until it felt right.
FWIW, mine always seems to shift later than normal when it is cold. When it warms up, it's fine.
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You must be FAST...
cuz you wuz FLYIN'...
when I PASSED YOU!
My "BARNEY" car