If I pedal hard, i.e. while standing/taking off/going uphill, the chain skips over the cogs making a load screeching noise and my foot just sinks to the bottom position.
I attempted to fix this problem so I replaced the crankset, cassette and chain with brand new Shimano Drore M590, Shimano Alivio HG400 and KMC X9 93 chain but the problem remains. I needed to replace these anyway since they are 2 years old and I had low quality components (i.e. drive side crank arm becomes vertical with pedal in bottom position).
I feel like either the free wheel or tension in the back derailleur is causing the problem. I removed the front derailleur because I only use the middle chainring.
I read all the other questions on this issue and they talk about the chain or the cogs being old but this does not apply since mine are brand new.
What is the likely cause of the problem in my situation? How can I make sure?