Trans check engine light

At what temp does this happen? Lots of places now freezing in the USA. How long must you wait after starting until you don't have a problem? 15 seconds, 10 minutes ?? When was the last fluid change?

It's happened when it's below 40s. Have to wait about 15-20 mins and it doesn't seem to do it. I just bought the truck a year ago but it was sitting. I'm not sure when the last time the fluid was changed. I plan to do it soon. Later this month or next

Try starting the truck daily, put it in gear, and see what happens. Sitting, not driving, often causes frustrating problems like that. Trucks that are often driven just don't experience such problems. Make sure you have clean fluid at the proper level. Consider changing the fluid. Your pressure switch had codes but latest start they didn't show up. Parking your truck on uphill/downhill slope may cause such problems particularly if fluid is low. Make sure your batteries are fully charged. Low voltage at the trans can cause all kinds of weird problems.

But I did notice that the fluid was pretty low. Not dirty though.