Torque converter not locking
 

I've owned my 92 Corvette for about a year now and have had it to a transmision shop but they couldn't fix it yet. The Torque converter is suppost to lock up at highway speeds (acording to books, over 25mph) but mine does not lock and when I step down on the throttle ging up a slight hill it gains RPM but not shifting down. Also the cruise control does not funtion and I think this may be related to the torque converter problem. Any help would be greatly apreceiated. Thanks