Thanks for the detailed instructions C32AMG! Here's what I have done so far....

"Adjust the cable as tight as it would go...." I still had early shifts

"look at the throttle lever, it should be touching the TV plunger..."
Yesterday I drained the transmission and torque convertor and replaced the filter and gasket. I can see the throttle lever and what I presume to be the TV plunger. (not quite sure what "TV" means). The plunger sits on the side of the valve body and the lever is held up against its end by a spring? This plunger looked like it was sticking way too far out of the valve body and when I pressed it in a bit to check its movement, it sprung halfway in and stayed there. Looks like this is where it's meant to be? Presuming that this could be the solution to the tranny's problem, I closed up, refilled and tested, but there is absolutely no change at all.

I looked under the car again and noticed that where the bowden cable enters the tranny, there is a plastic end to the cable which is loose and was stuck up and out of the tranny. (wish I could draw a picture!) Is this meant to be loose? It looks to be like it is making the cable too tight, but I can't see what should be holding it in place. I'll try to take a picture but it's difficult to get in there. Any ideas?