'05 Cleaned under the hood?
 

OK, cars been fine all this time. About 150K miles I checked for some codes with a new scan tool (new toy), noticed some general dirt under the hood so I squirted it off with some cleaner and a hose. The car sat for a few days. Went to drive it and went it fine at first, then after about the first 10-15 minutes it started down shifting any time I take my foot off the gas. I'm guessing a plug got wet that shouldn't have... Can someone point me to what plug or what it might be?

Unless you have a capable scan tool, you will need to check all the plugs. If one is not firing , you should be getting a check eng. lamp.
If you look at the part of the plug that screws into the engine you might even see moisture in the plug well before you even attempt to remove the spark plug.

Sorry, I guess I used the wrong terms. I wasn't meaning spark plugs. I was talking about electrical connections. All 6 spark plugs are firing fine. This was a shifting issue. Anyway, It's gone now. I disconnected the 3-4 connections I could get to (not really knowing what they do for sure) and gave them a shot of contact cleaner and disconnected the battery for a few minutes. What ever it was... it's gone now. But I'd love to know what it was... what connection doesn't have a water proof boot on it or is ripped or something.

A lot of the electronics in today's vehicles operate with only "millivolts" thousandths of a volt. The slightest bit of moisture can conduct enough to throw off a signal and the systems are so critical that things don't work.. That is what makes troubleshooting electrical problems on today's vehicles so challenging.
If I were to offer any suggestions, it would be to forget about washing the engine compartment of any vehicle with electronic controls..
It may be a little longer and require a little more effort, but just wipe it with a rag and be careful at that.

Yea, I guess I have to do that... the odd thing is I've done this cleaning 20+ times before and to every car/truck I've ever owned. Never had an issue. I'd love to know what the exact issue is so I can fix/replace it.

Most of us have also done that,,,,,,,,,,,,,,,,,,,,,,,with older vehicles that probably didn't have such critical electronics as part of their systems.

The first time I pulled one of those beauties was when I was finished cleaning the area under the hood, and the dash lit up like a Christmas Tree.
Now what????? Well in the process of checking many possibilities , the connections dried and things started to work again.
A valuable lesson, Everything under that hood is not moisture proof..

Do you ever wonder why some folks driving through flooded areas always seem to get stuck right in the middle?