You said the bike is 'new to me'. Is it a new bike, or a used one you just got? It almost sounds like something is heating up, expanding, and causing excess drag. Just a thought.
The frame was never ridden but is technically a used frame (guy built it up and then needed cash so he stripped it and sold me the frame.
All of the components are new but the pedals, rims, and saddle. Definetely sounds like what you are describing. I notice it initially but can pedal through it. After some climbs or extended mashing on the flats I have to work harder to keep my cadence up on the same gear. My quads actually start to get tired and then it just is too much. I feel like i am going at it 120% to maintain 80%. prior to that feeling the bike is butter. Quick to respond to acceleration. Everything feels stiff, smooth, and fast until i feel what I am describing..i feel like I am batty or something...like I need to take a large dose of man up but it isnt me guys.