Written by: Mike ErvinThe Throttle Valve Cable is attached to the throttle linkage. When the throttle is depressed, the cable is "pulled" progressively with throttle position. In addition to providing forced downshifts (kickdown), and progressively later (higher speed) upshifts at higher throttle settings, the throttle valve also adjusts main line pressure in the transmission. Operating a transmission with the TV cable out of adjustment, can, not only produce early, or late upshifts, but incorrect line pressure, as well. What this means, in simple terms, is that TV pressure that is too low, will produce main line pressure that is also too low, and will eventually "burn" the transmission clutches.
To adjust, on the throttle linkage you will have three
things attached if you have cruise, two if not. One of them is of course for the gas, the
one that is for the cruise control has a long slot in it (if you have cruise control), and
the other is the TV cable (which is actually a cable), this is the one you need to
adjust. Adjust the cable so that it will be pulled all the way, when the throttle is
simultaneously opened all of the way (with the engine turned off, of course). 
The way
to do this is, bolted to the manifold is a bracket which this cable runs through.
With close inspection you will see it has a sort of D shaped button you can depress and
slide the sleeve (cable housing) back and forth. The sleeve is what you want to
adjust, by depressing the button. Press the D button and slide the sleeve toward the
firewall as far as it will go and let go of the button. Now open the throttle to the
wide open position and release. You should be able to hear the sleeve click (rachet)
as it slides through the cable housing. Make sure that the cable returns (with no
binding) when the throttle is released. This preliminary adjustment will frequently be too
"high", and the throttle pressure will have to be reduced, to attain proper
shift points. I prefer to start with an adjustment that is "too high", and then
work down, rather than "too low" and work up.
To raise throttle pressure (and raise
shift points, and make "kickdown" more responsive) move the cable housing
towards the firewall (away from the throttle linkage), as you simultaneously depress the
button on the cable housing, move the cable housing away from the carburetor or (throttle
body) to increase throttle pressure. Move the cable housing adjustment a small amount at a
time (1 click or 1/16" or so), a small adjustment can often make a world of
difference. Naturally, to lower the pressure (and lower shift points, and make
"kickdown" less sensitive), move the cable housing towards the front of the
truck.