Why order a new cable? check the bushings in the cable under the hood. Pull the battery easy to see once you get it out of the way.
If the bushings are shot.
Booger Racing order up a set and save a bunch of money over a stock cable with rubber bushings that will just do the exact same thing in a year..
And there is a fill and drain plugs on the trans its self and at 9 years or so of service yeah its due.. ATF+4 in that T-350 some say use the conditioner some don't that choice is up to you..
Sounds like either a bushing issue or the synchros are starting to go bad..
Can you do the key dance and see if any other codes pop up?
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The silver 03 GT is gone, but a Solstice has arrived. There are three more PT's to play with though
My personal thanks to veteran and novice crewbies that have offered information and how-to's they have been instrumental in taking LiquidPT from modded car to stock to live a more quiet and sedate life.