When you had the CE Light on what codes or work was performed Mike?
Having a good state of tune, new fuel air/ filter, plugs/wires, clean throttle body etc can make the car run better/shift better as well.. sounds like u did some good work there..though..
When was the last time you changed the transmission fluid & filter? Dex VI (6) can make a nice improvement in shifting as well.
Quite often varnish builds up in accumulator/ valve bodies and solenoids. Did u use Trans Tune by Seafoam? It will remove help to remove varnish with normal driving & hwy combined and if shifts then improved, maybe new Dex 6 is now in order and allows you to see if there are any particulate matter in pan.
I am not sure on the 4t60e location of solenoids, I am sure another member will chime in soon.
I believe this is on your 94 Bonneville ..Can you please take a minute & update your profile please. This link will allow you to add the info quickly.-Thanks!