its just an old style mechanical linkage works just like a throttle cable. i dont have a rod from the steering column under the hood everything in the newer chevys is all in the column.

i cant get a picture of it because its tucked way up in the dash but its just like a throttle cable. it is mounted securely right by the shift lever, and whenever you pull it down to put it into a new gear, it pulls the cable more just as if you were giving the throttle more gas. and in turn it pulls the cable down on the transmission jsut as if it were pulling the throttle on the pump. but its running out of pull in the cable before it hits the last gear.

its pretty much just as if you were running out of throttle before achieving wide open throttle

i hope i explained it ok i tried my best

 

yeah i grasp what your saying... it isnt like an old dodge column with a little lever that rotates at the base of the shaft. only thingi can think of it to set up your own lever system that is controlled by the cable... regardless the cable is only going to move so much, therefore you have to make something that will cause the gear selector to move more, with less cable travel... i'm going to draw something up that i just thought of and attatch it here in a min

 

or you can go with the 2nd option that wont require you to change cable orientation