Weird shifting on a 82 300 SD
 

I have recently purchased a 300 sd "82" and it shifts into 1st almost before it gets moving --then when it shifts to 3rd it will go in and then kick out totally - as the engine revs -- if I lift off the accelerator it will then catch 3rd and everything behaves as it should-- also -it shifts down when on the hyway just fine " passing gear"-- I am thinking it is the modulator- but I cant find any info on the specs -- or do any of you have any suggestions?
P.S the car is cherry in all other ways and only has 160,000 on it.

I think that this article will be helpful. Pay special attention to the part about Bowden cable adjustment.
http://transmission.articles.mbz.org/adjust/