Transmission does not want to shift up, stays in low. reverse and neutral fine. on 1996 Chevrolet G Series Van (G30)

Fluid level is where it should be.

its freeeeeeeeeeeeeee
2 more answers , 1 more comment
seek to diagnose it like AAMCO transmission
It's likely a speed solenoid. They generally go bad from normal use over 20 years. You should replace all of them at once. There are 3. They are simple to get to under the van and easy to replace.

The connectors may be bad as well. The whole process for solenoids and connectors shouldn't ve blmuch more than 150-200$

where are the 3 speed solenoids located, I see two that are the same and there's a large plug with 11 wires going to it next to it