1991 Cadillac Deville wont go into park

I brought my car to a local auto repair shop. They did a few repairs to it. One of them was to install new transmission lines. Well I got my car back and everything was fine until the next day I noticed it was leaking antifreeze (water pump repair). I brought back and they tightened up some hoses and told me to pick it up the very next day. Well I picked it up after they closed. Upon leaving I noticed the car was moving slow but brushed it off. I went to a friends house a mile down the road and went to park the car. It wouldnt go into park. I shifted back to drive and back to park, then it went into park. As I left her house an hour later I went to back out of her driveway, there was no power. I thought I was slipping on ice but eventually it went. I went 3 more miles down the road and again noticed the lack of power. It kept acting like I was very low on tranny fluid. I arrived at the store and went to put in park. I couldnt, in fact it wouldnt even go past reverse. I tried for 20 mins. I brought it back to the repair shop. They looked at it and said the colum was fine, but it was the trans. My question is what happend here. My trans works fine and the next day its messed up after they look at it. They deny any wrong doing but I dont believe it. A friend of mine says that when they changed my lines they may not have gotten the air out of the tranny and because of that it messed it up. I spent $2000 on repairs and now my trans is broke. I dont know what i'm going to do now and I have no more money. Please help