O/D off light blinking

Hey everyone!
I have a 1990 Toyota pickup that I bought about a year ago. I drove it for about a month and then one day at a stop sign it lost all of it's power and felt like it was skipping second gear and the O/d off light kept blinking and then the AT oil temp light came on and kept overheating. I brought it to a couple of transmission specialists and one guy said nothing was wrong except for a connection so he changed that. Then it drove for about 3 days and the exact same thing happened. I brought it to a different specialist and one of the solenoids was fried.. then it all happened again so one of my friends who works on Toyota engines and transmissions thoroughly went through everything, noticed the same solenoid was fried. He changed that, lengthened some wires and changed the transmission computer thinking that maybe the computer was sending too much to the solenoid. Other than the solenoid he said everything looked great. 6000 miles and it's been running like a charm... Then today it happened again! Same exact thing except now there is no second gear at all.. does anyone have any idea what is going on?