One night and it started not to shift

Hi guys, I'm having a big problem with my Rodeo. I was driving one night and it started not to shift. It happened very quickly and I had to park it immediately and have it towed. It was in a repair shop and they took a look, said it was electrical transmission and had to go to a transmission shop, where it's been for 3 weeks now. They've torn apart the transmission twice and put it back together twice. They did find a problem with a solenoid (?) And said it was telling the Rodeo to go in reverse at the same time it was trying to go to 2nd. So they replaced that. They said it's better but when it heats up, after driving for 30-40 minutes, it 'loses pressure'. They were thinking electrical. So they had an electrical specialist come in and test. They found nothing. So they had replaced everything that they thought might have a hairline crack in it. Still the same issue. They said they would replace the pump, but didn't really think that was it. So that was the last I heard, 3 days ago. They are so great for trying to figure out what's wrong with it, but I really need some help. I'm sure they're trying everything they can think of but something is slipping by them and the cause of the problem is not manifesting itself. Any ideas or have you heard of this situation before? I know they're trying everything. I'm just hoping for a clue. Thank you!