My 91 volvo ia also getting hung in the 3rd gear. it takes about 10 minutes.

mostly likely overdrive relay, far back right in center console where fuses are in front relays in back, my 1992 wagon the relay is yellow. if good at sodering it can be repaired, about 45 buck new check fcp groton. One way to check if relay, turn car on but not start depress the od button on gear shift level you should hear a click in the console and underneath the car and the arrow will light up on your dash - if you hear no click or dont see the arrow relay is dead. The relay solenoid also goes out too, but you will see all the stuff I just mentioned actually happening but no sound by the tranny- solenoid can be bypassed - fcp groton can sell you the bypass for about 50 bucks - if you bypass you will a simple 4 speed automatic- lots of info on swedishbricks.com to get you clear on everything I just mentioned