Transmission not shifting?

My car will not move in first gear once warmed up. Works okay cold. Took out solenoids and cleaned filters in one. Only one filter had any trash and was not totally clogged. All tested to work. When I put them back in and ran the car, it shifted normally when first driven, as though this fixed the problem, but D4 light was flashing. Once it was restarted, the D4 light no longer flashed and shifting went right back to not having first gear. Other gears shift normally. Have to manually select second to get going once the car is warmed up. It will not go when first is manually selected either. It can be put in first but barely can move much at all even when revved. Acts like torque converter has no fluid when warmed up or that fluid is too light a weight. First gear only.
Just got car for junk price, from "little old lady" who did not drive it much and knows nothing about it or what she might have done or had done.
Gambling that it can be fixed without spending a fortune.
Reset ECU by pulling battery cable. No change.
How will overfilling affect this? Dipstick shows it to be way over full. How much I cannot tell.
Engine light is on. Transmission fluid looks like new, red and clean and no sign of debris. Donot have any idea of what kind of fluid is in there.
This is DIY only project. No shops or dealers, so exact and correct answers are needed and appreciated.
Took car to parts house and had them run their scanner. It returned the following codes:
P1491 - Emissions.
P0705 - Range sensor circuit malfunction.
P0706 - Transmission Circuit Range/Performance.
These seem to indicate Neutral Safety Switch problem.
Swapped the old switch out for a new one. Set it to click (neutral) and installed with transmission in neutral. That took a couple of tries to get the gearshift lights to come back on.
Result was that it operated exactly like the old switch - no first gear, no matter if D4, D3, or first gear is selected. Information found, as well as diagnostic codes, all direct me to the "neutral safety switch".
Still have no first gear. How to get it to work is the question. First gear only works when the car is first started and the fluid is cold. Once warmed up it does not. No problems shifting between other gears once first is bypassed. Having to take off in second then shift to D3 and/or D4.
Can overfilling the fluid do this? Which solenoid can cause this?
Neutral safety switch does not look like it is the problem. Even though the error codes pointed to this part as the issue, replacing it with a new unit did not fix problem. Click stop is not audible. Can be felt when devices are rotated, but not heard. Car will not move until this click is set.
The car runs fine escept it has no first gear after initial warm up. It will only pull the first few minutes while the fluid is cold. Might this be the indicator of what the problem actually is? If it can pull with cold fluid, then the transmission itself is probably not bad.
Can overfilling the fluid do this?
Is it possible that a solenoid is the culprit? If so which solenoid(s) can cause this? Please post diagram. Only found one that had screens/filters. Cleaned it even though it was not dirty. When it was put back in, the car drove normally on first startup but the D4 light blinked. I restarted the car and the D4 light went out and so did first gear.
Fluid is healthy red.
Need information for this model with this exact problem. Did extensive searching on web for information on this without success. No information on having first gear only, not working.