Look for and compare end shaft side movement, just because the new
mower does not vibrate does not mean it was built as well as the old
unit. A New blade would be the cheap and easy way to confirm a bent
shaft or a loose tolerance on the main shaft bearing , that vibrates
with a poor blade, plus you only have one blade now. I just threw one
away that seemed balanced off the mower, I thought the shaft was bent.
It does not take much to ruin a blade.