Your chain or cassette might just be worn out. Feel free to buy an expensive light weight derailleur for a 38 pound bike, though.
Cassette and front sprocket are both done, my 44 big ring only has about 20 teeth due to it being used as a bash guard. Plenty of big drop freeride/DH guys swear by the X.0, although I'll probably digress and roll with the X.9 for cost effectiveness. I'll be replacing crank, bottom bracket, shifters, front and rear derailleur, cassette and buying a proper big ring bashguard so I can save my shit from losing teeth in the dinosaur steps by the riverfront.