What is OBD codes 731 700 and 730?

I just got a used 06 Grand Jeep Cherokee with 72K, and after I took it to my mechanic, he plugged in his diagnostic machine and the codes 731, 730, and 700 all came up. The engine light was on as well, I guess they reset it at the auction, I it purchased with a dealer. I know these are all transmission errors, is this serious ? What kind of damage could it possible be. I no longer trust this dealer so I would like if there is a way he can possibly mask what is wrong, because he wants to go to "his mechanic" not mine. Thank you so much for this help. Stressed outta my mind.