What did I do to my tranny?

[Heavy87Chevy]

Hey guys,

So I put my truck into a ditch, if you could even call it that, a week or so.. I was able to get out in 4wd but when I was back on the road she wouldn't shift out of 1st gear.. I checked my transmission fluid which was very low & filled it up, unfortunately that didn't help at all. Its an '87 K10 with a rebuilt 350 & 700R4 trans. I don't know much about transmissions, or these old trucks in general so if anyone can help me out before I just get my wallet out & take it to my old man's transmission guy I would greatly appreciate it!