That is a pretty good sized drill, and I don't think that the Haas has enough torque to turn it. What you lose in a machine using a VFD is torque multiplication: not enough gear ranges to get the motor into its rated horsepower/max torque range, and so not enough current can be sent to the motor, even though it demands more (without damaging something).
If using a geared head, in low gear, I think you need to have the spindle turning about 450 rpm to get max torque. Because the drill is such a large diameter, this speed is not possible without burning the corners off the blade.
I suspect you'll need to open the hole with maybe a 1.5" drill, then rough it larger through interpolation. Spade drills don't start too well in a pilot hole.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)