Hello,
Once again I have this issue for like 3 years. Trans would not shift from 2nd to 3rd on slow speed by default, it would go into neutral and after I give some more throttle it would downshift to 2nd. If I get to 40 mph or similar, once I release throttle pedal it would shift to 3rd and after that everything works fine - no problem at any speed. So my guesses are that something is stuck in valve body or governor.
Until now filter has been replaced, fluid flushed (was red even before flush), TV cable adjusted, bands adjusted.
The reasons why I suspect on governor valve is that this seems to be related to vehicle speed. Why I suspect about it sticking is that once (or twice) times the trans gets into 3rd after driving at greater speeds, it will work fine until i turn of vehicle and leave it for 3-4 hours, sometimes less sometimes more.
I also remember that once I got stuck in some pond and engine turned off because of hydrolock, so trans spent some time in water. After that the problem was gone, and it reappeared after two months. I immediately flushed trans that time but there was no water in it however. Could it be that there is some crud that block weights in governor and make it stuck sometimes? Am I missing something or the problem is probably governor?
I've also noticed that when the car is cold (like if i leave it overnight) the trans shifts from 1st to 2nd at later rpm on same throttle applied (like shifts occur on 2100rpm when cold and bit below 2000 rpm when warm)