The gear catches, but when I accelerate backwards there is a grinding sound an no motion, is it a solenoid problem or is it something entirely different?

Hi I used my computer on my truck and got a code PO756. I first noticed my tranny not shifting correctly so checked the fluid it was low topped it off ran fine then did it again same thing reverse was sluggish then first was sluggish checked the fluid it was low topped it off again then it did the same thing reverse was sluggish but drive seemed fine till I got around 45mph then wouldn't shift noticed I had a leak so I used bars leak for transmission put that in topped it off with fluid shifted fine in drive till I had to slow down then wouldn't shift at 45mph got home next day went to back up heard a clunking sound backing up drove it same thing used my computer on it gave me codes PO756 and PO730 which said 2-3 transmission solenoid problems no 1-2 gear the other code was incorrect gear ratio so erased the codes nothing changed same problems now it acts like there is no reverse if I park on a little hump and hit reverse I can back up for a little ways but revs up high took it for a drive keep getting the same codes. Does that mean I will need to replace the transmission solenoid and if so will it fix reverse?