Mercedes: 1987 Diesel Mercedes gear shifting problem, diesel mercedes, throttle linkage

Question
Very recently my 1987 diesel MB has been getting stuck in gears.  It's like I've set the cruise control; even though I've taken my foot off the gas, it continues at the same speed for ~0.25 miles until it suddenly jolts back and begins slowing down.  Is this a problem with cruise control?  A vacuum?  
Thank you so much!

Answer
Answer:
This could be a:
* Cruise control fault?
* Throttle linkage fault?

It is a potential safety issue.
Best advice:
Take it to a local independent MB shop as soon as possible.

Good MB Shops
http://www.mercedesshop.com/shopforum/forumdisplay.php?f=14