I have successfully resoldered two cruise control and two climate control boards. It is really not hard at all, just open the case and touch each connection (solder point) with a small hot soldering iron until the solder boils; add a little more if needed. Make sure the solder does not run on any nearby connections. Take your time, there are about 100+ points to hit.
The surging comes from a weak connection where the solder cracks and does not send a signal until it reaches a higher amperage, and by then the speed will have dropped sufficiently that the system surges to get back up to the set speed. Works pretty much the same with other conenction problems. My 85 300SD system would have given me whiplash if I keep using it as is.
This link is to a picture of a point I subsequently redid. You can actually see the cracking, but just because you can't does not mean it is not there.
http://www.peachparts.com/shopforum/attachment.php?attachmentid=46327&d=1185425015
Just touch the hot tip on there until it melts and the crack is gone!
This link is to a DIY resoldier thread.
http://www.peachparts.com/shopforum/showthread.php?t=86958