ATX shifts hard. Solenoid?

[AutostradaVR4]

The auto trans on my SL has been shifting hard and jerking lately, and the other night it wouldnt shift into 4th at all and I got a CEL code having to do with the transmission solenoid. So to my question; how hard is this solenoid to replace, and were is it located? Also, anyone got a part number?

Additionally, I check the fluid every few weeks so I know thats good, and it seems to get worse (more jerky) when its hot.

[Stealthee]

Not shifting into 4th sounds like the end clutch. The overall jerkyness sounds like clutch packs are worn.

[AutostradaVR4]

hmmm...
these things are effected by heat?
becasue honestly, when i first get in it in the morning it's fine...it's only after ~20 minutes of driving, once the trans is good and hot, that it starts to be real jerky on the upshifts and acts like it doesnt want to disengauge when im coming to a stop.

and the not shifting into 4th, it only did that once, after some aggressive driving. The other gears were weird that time too...it almost felt like they were slipping.

[Stealthee]

Hate to say it, but it sounds like its on its way out.