1997 pontiac trans problem

I have a 1997 pontiac grand prix with a 3.8 liter v6 engine, and my trans occasionnally seems not to want to shift from 3rd to 4th it eventually
shifts but its later than it use to shift. I was thinking that it may be the shift solenoid,if so can it be replaced by just removing the trans pan or do the trans need to be removed from the car . Also is it just one solenoid or are there several. If the trans do not have to be removed do i just drop the pan and replace the solenoid. thanks for your help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.