tranny sensor???

I have a 96 cirrus and when i shift from reverse to drive it takes more then a second or 2. Then it kind of clanks a little bit. I think the little bit of a clank is just from the rpms being up. Then going in to drive. But I was told that the transmission sensor could be bad. I have no idea.also when i put it in low it will not go then it will kick in and go with a bang,but other then that when it is in drive it takes off fine drives and shifts good. I would appreciate any replies thank you, Jason