1985 300DT engine Intermittent RPM surging, won't shift out of 1st gear
 

On two occasions, the engine will surge while driving and not shift out of 1st gear. If the car is stopped and turned off and restarted, it runs normal. This has happened twice in 4 months. The car has 200K miles. The accelerator pivot mount at the firewall was recently replaced the first time this occurred. Any ideas or thoughts on possible causes would be greatly appreciated.

Thanks for the lead...I will inspect the boot for leaks and wear