Ok. First a little background. My 2001 Z has 166,000 miles and I am the original owner. Mods are boltons but no headers. About 6 months ago I got HPTuners and did some tweaking on the tune. Prior to that I had a Vinci handheld. As part of the tune I copied a file that increased line pressure in the tranny to let it shift quicker and slightly firmer. Life was good.

Now the issue. Last weekend I was merging into traffic, running about 30, and kicked it. It dropped down as it always has but then it stopped pulling, the revs came up, I backed out and it shifted. Since then the only way it will shift out of first is to let off of the throttle. 2nd to 3rd shift is fine but no more OD. I also do not have reverse.

I searched around the web for issues similar and initially I didn't realize I had lost reverse so what I came up with was possibly the TPS. Changed it out with a known good one, started the car and that's when I noticed there was no reverse. Swapped back to the original TPS and same issue. I checked the trans fluid that night and it did not appear burnt. This afternoon I was looking around and decided to check the radiator. No visible liquid when I remove the cap from the radiator itself and the tip of the reservoir dipstick was just barely wet. Reason for. checking this was I had read that the cooler could rupture and cross contaminate. The fluid in the tranny appears ok but I have a very limited sense of smell and cannot determine if there is any coolant mixed with the trans fluid to rule that out as a contributor.

So my question is what would cause the shifting symptoms described above? Any help would be greatly appreciated.

 

Your missing 2nd, 4th & Reverse.....Broken/Stripped Sun Shell.

When you "let off" for the 1-2 shift.....It is actually shifting to 3rd.

 

Yup. GM updated and strengthen the sun shell around 2003, but too late for you.
Considering the trans is 15 years old and the stripped sun shell likely shot metal shavings all over the place, you will need a complete rebuild or replacement.

Many/most will say to also replace the converter as metal shavings cannot be cleaned out of it and that will contaminate the new converters. Alternatively, especially if you have an expensive aftermarket converter, it can be sent out to be opened, cleaned and re-welded for about $150 plus shipping.

 

^^^This........

Your sun shell broke/stripped. Time for a rebuild...

 

Thanks for all of the responses guys! I was hoping for something less expensive but I guess now would be a good time to upgrade the tranny/converter or to do a six speed swap. Thanks again!