Shift cabe broke next to transmisson

The shift cable is located under the transmission, usually on the passenger side.

on the cable there is a release on the cable lift up the lock put trans in park and the shifter in park then lock it into place

The 1985 GMC Sierra transmission is a th700R4 overdrive transmission. The 700R4 does not utilize a vacuum modulator. Shift points are controlled by the T.P. or kickdown cabe. Proper adjustment of this cable is critical to transmission longevity. Your Pontiac, if originally equipped with a th400 transmission, has no means to connect this cable to the carburetor. I would not recommend this transmission swap. Also the th400 and the 700R4 use different sized drive shaft yokes, so your drive shaft cannot be used.

you may need to remove the air box to able to see the transmission range sensor . with air box removed look for the shift cable and where it attaches to the transmisson shift arm . the range sensor should be right under the the shift arm and where the cable attches. It should have a 15 mm bolt on the arm and 2 13mm bolts holding down the sensor . the sensor is adjustable so try and make sure you put it back in the same position

Check a part thats mounted on the drivers side of the transmission called the inter lock switch It could be a shift cabe adjustment but the cable has to move the interlock switch every time you shift the vehicle and is the most likely part to start binding and causeing shift problems and a number of other issues with control functions with vcm operation and false code readings set off

If one cable is broke it won't shift right noy need to repalce the cable and cable housing then adjust the cable so it shifts. With the cabe broke it is trying to shift into 2 gears at the same time.

How about a trans filter change? That works when things like this happen.

the kick down has to be adjusted after replacing the kickdown cable go to http://www.alldata.com to get the correct proceedure for the 700r it is a common problem for those transmissons.

you have a torque clutch problem chan your torque transmission

First place to look is to make sure that when you move the shift lever, the shift arm on the transmission is also moving. If the cable between them breaks or streches, this will not happen...If you find that it dosen't move properly, change the cable!
Hope this helps...likely anything else will be much more expensive!