I had that happen in my 98 v6. I took it into the shop and it turns out that the 1st to 2nd shift solenoid was going out or at least it showed a fault. When they got inside of it the solenoid was actually punching through where the spring and everything is set inside of the transmission valve body. The fix was a new solenoid stiffer spring and a sleeve where everything sits in on the valve body since then I haven't had any issues. It may also be from low transmission fluid or dirty transmission fluid. When was the last time the transmission was flushed
changed the fluid and filter when I bought the car about a year ago, I still need to scan to see if I have any codes or not, I have a 7015 SCT, we'll see if anything comes up, this morning no light and did not have the light when I drove home last night