1991 740 During the past three weeks, my lock-up torque converter has failed 3 times during travel on highways: once for 5-10 seconds, and two times for about 30-45 minutes until I finished my drive. Each time during failure, the cars goes back into 4th gear. If I turn off the car for an hour or two and then restart, the problem disappears and does not happen for the rest of the day or week until the next time it occurs. All shifting and downshifting for gears 1, 2, 3, and 4 appear to be normal. The car has 150,000 miles, has had all recommended maintenance, and had a new Volvo transmission installed one year ago. Can someone please tell me what exactly the problem may be and what it will take to fix it and how much money the repair will cost? Thank you.