How to replace shift solenoids?

Well when I had bought the car the man had it checked thoroughly with paper work. And recently I went to get the shift solenoid but that day and say prior my car would actually stall in the middle of driving it. So I had bought the rear and front crank shaft cam. However, I just needed the front. Rear sort of made worse with the jerking. Which leads me back to the solenoid. While driving though especially freeway mph and I am having to slow down it jerks and than when I am putting car into drive, almost as if it is skipping first and auto goes to second, the rpm go a little wild. And only does while in automatic. Being I can drive as manual as well, if driving in manual though, the cars perfect.

I have a 2000 maxima, the car would not shift to 4th gear and the overdrive is not working. I replaced the transmission with a 39,000 transmission from an accident car and I am still getting the same code saying the transmission solenoid is faulty. Is there another thing I should check before I send the transmission back to the junkyard. Note the other gears shift okay.

The transmission solenoid itself is what allows an automatic to shift into the overdrive gear it would be a lot cheaper just to change this first.