Chevrolet: 1989 Chevy Van 20 transmission, chevy van, different gear


Question
1989 Chevy Van 20 transmission
My van will no longer go faster than about 25 miles/hour.  It does fine at low speeds but I think the problem is that it wont shift into a different gear at about 20/mph or so.  How can I troubleshoot further?  

Answer
Hi Adam;
      Well the first thing I would do is drain the trans. fluid and replace the tranny filter , and look at the fluid to see if it is burnt , dirty , etc. than with a new filter and fluid see how it is. and look to see if any line or linkage came off the tranny, or by the fire wall. ok