Check your drill bit. I recently had a 5/16 drill that I for the life
of me could not drill a hole. I kept running it slower and slower.
Finally pulled it out of the chuck and looked at it figuring it most be
duller than a spoon(even though it was brand new).

Looking at it, when it was ground it must have slipped as one flute was
all botched up. The relief had wiped out one cutting edge.

Maybe it got munged up when it was ground, or it's dull, or you running
it too fast. Or a combination.

JW