tranny problems 88 K5 Blazer need help

[WyoDenali]

I have found a 88 K5 Blazer for sale. In talking to a relitive of the owner. He said it sat for about 2 months. Now it will not shift our of 1st gear. it is a 700r4 transmission, The guy said it seems strong but just will not shift out of first. I am wondering if it could just be something easy to fix. Modulator or something.

Thanks

Tim