Why won't my 1989 jeep shift out of first gear?

[Joshua]

I have a 1989 jeep strait 6 2 door I was coming home from Detroit and it won't shift from first at all. I had some work done to it and if I red line it it will shift to the next gear but that's it. I had a trans place look at it and they told my it was the electric part of it but I can't find any thing wrong with it please help me with it