Trans?

I own a 2000 automatic mustang with 132k miles and ive been trying to sell it, however all the sudden it doesnt want to go into drive after coming out of reverse after anything longer then a 15 min drive. Before this it was having trouble going into 4th like it would rather run at 3k rpms insted of shifting, and then when it shifted there would be a lag between gears. But before all this one day out of the blue i went to make a U turn and it lost everything except 2nd low and reverse. It eventualy kind of worked itself out and I took it to aamco and they couldnt figure out what it was so i figured id see if anyone has any deas? or has had the same problem? I dont want to sell it anything wrong because otherwise its an awsome car and I wana try and make what its worth.

Like when i take a semi long drive and have to make a u turn, like yesterday i went 2 mcdonalds and when to pull out but after i went out of reverse into drive all it did was rev like i was in nutral. Then it doesnt stick into 1st low so i put it in 2nd low and have to drive it like that untill I let it sit for awhile and then i can drive it again

Yea i had the trans fluid and filter changed about 3k miles ago. I know they put in castrol fluid and a high milage suppliment. Ive checked it a few times and its right on the line so i know the fluid is fine

Yea i took it to the ford dealership down the road and they said it needs a new solenoid and down shift cable. Which is believable because half the people i talked to said it was probly a solenoid and one of my friends said it sounded like my downshift cable was bad.