RE: slow take off
No one has mentioned changing your spark plug! and don't think cos it's new it must be good; I've lost count of how many new plugs I bought over the last 25 yrs that were bad out the box.
Also check your coil, I had a YZ125 years ago that seemed all choked up off the line then would clear itself...bad coil was the problem.
By the way is your DDM a torque pipe or top end pipe?
Bad crank seals will give lean mixture on the bottom end that can cause bogging off the line
I've learned to always do the easy, cheap stuff first then work up from there. Mixture, plug, compression test, clutch, then gaskets, carb, coil, mag etc.
Why would you buy a new motor once you have a crankcase- just rebuild it, if you just quit and buy a new one you'll never learn how to diagnose and fix a bad one.
Just my 2 cents