Transmission has around 5,000 miles on it. It was built to handle 600whp. It has an FTI 4,000 stall in it. The only way the car will start in 1st gear is if the shifter is in OD. It will start in 2nd in all other gear selections. It will also not down shift into 1 manually. If I floor it in OD it starts in 1st bangs 2nd as it should but won't tach over 4,000 rpms. If I pull it back to 2nd around 40mph, it pulls all the way to 6500 and shifts like it's supposed to. Any help is greatly appreciated. Thanks in advance. The car is a 98 trans am.

 

Those are very strange symptoms, which makes me suspect the Manifold Pressure switch (MPS).
The proper thing to do is connect a scanner which can read the shifter position (thru the MPS) and shows which gear is being commanded by the PCM.

I was never able to confirm it, but I once had the "won't tach over 4,000 rpms" happen to me at the track. I think the trans temp got too high. Again use a scanner to read the "supposed" trans temp. The sensor is also in the MPS.

 

Thanks. I ll do that today.

 

Scanned it and it's showing the car is in 1st gear with any gear selection.

 

Then assuming your shifter cable is working, it is sounding more and more like the MPS.
It is easy to replace after dropping the pan.
This thread has some similarity and might be useful to you:
https://ls1tech.com/forums/automatic...l#post18817472

The OP's idea to remove the connector and confirm the trans starts in 3rd gear is a good one. It just hard to remove the trans connector on most cars without dropping the trans a bit.

 

Double whammy of MPS. This is the second likely one in a week.

 

Thanks fellas. Ordering an mps tomorrow morning. I ll update the thread when it's fixed.