I don't work on automatics... just never spent time with them... Here are a couple things which come to my mind. If you've tried them or they're simply not applicable well, at least you got a free bump out of it.
Have you checked your transmission fluid levels? I suspect whoever said "linkage" may have been referring to the kickdown cable inside. It's accessible by pulling the pan but you'll need to drain everything first. Is your speedometer working? Have you checked for diagnostic codes?
Here's a link to Toyota's service manual's section on the auto:
http://www.cygnusx1.net/Supra/Librar....aspx?S=AT&P=1