98 Century won't shift

Hi guys,

Here's the problem I have on my 1998 Century, 100k: transmission won't change the (upper) gear. Simple as that... No matter how high the rpm is it won't change to the 2nd gear. No matter how hard to accelerate it. Is does this in D, 3, 2, 1. I went up to 40m/h and no shifting. R, P, N work fine. Is there anything else I should check before I go to the shop (and look stupid)? So far:
- I changed the oil and filter
- I changed the vacuum modulator.
- I didn't check the vacuum pressure though (there is vacuum)
Is this one of the symptoms of a bad solenoid? Any other ideas? Thank you.

Needs to scanned on a trans function scanner where the shifts can be commanded and confirmed, also loo for a bad tps, but that would set it's own code normally.

Needs to scanned on a trans function scanner where the shifts can be commanded and confirmed, also loo for a bad tps, but that would set it's own code normally.

I guess that can only be done in a shop...