The cable is there behind the air cleaner. It adjusts with slides held by screws. Making the cable a bit tighter will give you some relief. But even so, mine upshifts at strange times, like when going up a hill and giving it gas. A 3-2 downshift seems impossible to get unless I floor it. I attribute it to old age, since its fine otherwise.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma