2002 Honda Accord: Trouble downshifting when hot

I have a 2002 Honda Accord. Well maintained with 160K miles. It runs fine except when its been driven for roughly 3 hours at highway speeds. It has trouble downshifting when I try to pass. When I hit the accelerator it jerks and won’t downshift. If I slowly accelerate it will shift, but not well. The check engine light comes on at this point. The code it throws is P1739 for the 3rd clutch pressure switch. It also throws a code for the shift solenoid, which I think it probably the real problem. My dealers says $200-$300 for the solenoid. Will this fix the issue and is it something I could replace myself?

I would trust your dealer for the $300 max charge to replace the solenoid. The part is generally internal so I would guess that you don’t have the resources or time to replace it. I would also guess from the price that you are a loyal service customer to this dealership and if so there is no point messing with that to save a hundred bucks.
I believe you are being treated with honesty and should go ahead with the replacement.
If the replacement doesn’t work, I bet your dealer will work with you in taking the next step if you feel you will always need to punch the gas in order to pass cars on a three-hundred mile trip.

Thanks for the quick feedback. The $300 is only for the part. From what I can tell from my repair book, there are two of these solenoids, both of which are on the outside of the transmission. I’ve tested them with my multimeter and they both meet spec, but that was while cold. I’m not sure if this is a problem that is even worth trying to fix. Advice?