Good afternoon, I have a well-travelled 1997 C2500 with the 7.4L gas engine and automatic transmission. It has ~380k miles, but generally the more this truck works, the happier it is. I have a multitude of ****ling problems that I am finally in a place to get taken care of.

The subject of today is the transmission.
I have had a few occasions where the transmission was slow to engage if I tried to drive off after a cold start. Once it had warmed up, there were no issues whatsoever.
I determined that this happened because the transmission fluid was a bit low. Upon topping it up, the issue went away.
This issue has cropped up more frequently of late, and now that I have moved from Florida to Michigan, the cold seems to make it worse. Now I have to top it up maybe once a month?

The weird thing is that the transmission fluid is bright red. There are no red puddles under the truck, ever. Where is this fluid going???

One of my other interests is antique tractors. When the seals on a Farmall Cub hydraulic pump start to go, it pumps the hydraulic fluid into the engine crank case and your oil level goes up. I must assume something similar must be going on here? I do have engine oil leaks as well, that have *maybe* seemed to slow down? Hard to tell. I do not see any red tinge to the engine oil, though. And the antifreeze is orange, so hard to see if it's somehow ending up there.
Now that I think about it, I believe the radiator has 6 connections: coolant in, coolant out, heater core in, heater core out, and two smaller connections for cooling of.... transmission fluid? I don't remember now. I'll have to look it up. Maybe I just answered my own question and I'm leaking transmission fluid into the radiator? I don't see anything in either the coolant or the transmission fluid that doesn't belong there. Not sure if the transmission fluid would be insoluble like engine oil would be.

Anyway, does anyone have any ideas on where this could be going and what to look for?
The other thing that concerns me here is that the last time I had to top it up, the transmission was behaving *very* badly. But when I topped it up, the fluid level was only a little bit below where it should have been. Again, the problem went away once topped up and warmed up. Maybe it was extra sensitive due to it being *very* cold at that time?
I'm overdue for a transmission fluid and filter change. Could a fix be as simple as that?

As a secondary, transmission-related but not fluid-related question, I have a lot of play in the transmission selector. I often have to move the selector past the gear I am shooting for in order for it get the gear I need. Since I cannot go past Park, I am unable to get into Park. It only goes as far as Reverse. So now I park in in Neutral and set the brake. This has been this way for a while, but is getting looser. I need to get this taken care of before it lets go completely.
The shift cable obviously connects to the selector somewhere in the steering column and to the transmission underneath. As I understand it, though, there is another intermediate connection under the carpet near where the cable passes through the floor?
I know there is an adjustment mechanism where it connects to the transmission, and I was expecting that that had come loose. However, when I crawled under there, that all seemed tight and proper. I guess my next step is to start taking the steering column apart to see what's what in there. Any thoughts on this would also be appreciated.

Thank you in advance!