[etmx183]

You can use the original bolts over again BUT grind a small bit off of the end of the bolts. New bolts are recommended due to the stretch of the bolt hitting the bottom of the torque convertor cover. This will cause a dimpling of the end of the convertor backing plate affecting the lockup clutch in the convertor from having a flat surface to grab onto. This will cause premature convertor clutch failure and debris contamination into your transmission. A single drop of red loctite should do the trick.

This from ATRA website.
Never use an impact gun to install torque converter bolts. Driving a bolt into the converter cover will create a dimple on the lockup apply surface.

Lockup clutch failure will occur when the lockup piston applies against an uneven surface. Grinding off one thread length from all lockup converter bolts is recommended to avert this type of failure.