1. The 10x0 series (Pascal GPU) decrease the hashrate with every new DAG Epoch - the bigger the DAG - the slower the GPU. I think you see old results. If you mine another coin - ETC for example with only 3GB DAG compared to ETH with near 5GB DAG - you will get 40mh again.
2. you can push the card a little bit with higher core clocks to get the hashrate back, but for sure the power consumption is also higher.
3. don´t play with PL. PL - POWER LIMIT - why setting this? There is no reason. Set a fixed core clock and fixed voltage for the GPU - you can get better results, it is more stable and it makes more sense.
I confess I didn't know about the reduction because of epoch
A suggestion to OP, try to use Nicehash:
https://www.nicehash.com/Let the program benchmark all the algos for you and all the miners, at least you will know which one is most profitable to you
If you can achieve more hashrate with ETC for example, you can mine ETC and change for ETH if this is your goal
With Nicehash you can mine and receive in BTC
Obs - I suggest this because it's easy for you to start, after some time you can mine directly in a pool when you get more knowledge