93 diesel with auto, shifting problem
 

A buddy of mine has a 93 Chevy with a diesel and automatic. The transmission was recently rebuilt. A couple weeks ago he was hauling firewood and it downshifted to 2nd going up a hill and since then it won't go past 2nd gear. It shifts fine between 1st and 2nd up or down, just not making it into third.

Any suggestions on what to look for? The guy that did the rebuild said he checked it out and it has to be something internally and to pull it out and bring it in for tear down. Thought I'd check here if anyone has an idea.

im not very good with trannys but since a 93 is a mechanical 6.5 the tranny isnt controlled by a computer. maybe something with the kickdown cable. im assuming the tranny guy didnt do a good job or something like that.