We present the discovery of sub-stellar mass companions to six giant stars by the ongoing Penn State-Torun Planet Search conducted with the Hobby-Eberly Telescope. Each system has a single planet, with minimum masses ranging from 0.9 to 5.3 MJ and orbits ranging from 0.9 to 5.6 years, the longest period yet found by our survey. Three other stars exhibit long-term non-linear RV trends, indicative of additional companions that may be low-mass stars or brown dwarfs. If these companions prove to be substellar, they add to a growing number of companions to giants that have minimum masses in excess of 10 MJ, making them candidates for either brown dwarfs or supermassive planets. Such systems may require a gravitational instability in the circumstellar disk to form. The two remaining stars have significant RV noise due to intrinsic stellar variability, making it more difficult to detect a low-amplitude periodic signal. If the noise component of the observed RV variations is due to solar-type oscillations, we show, using all the published data for the substellar companions to giants, that its amplitude is anti-correlated with stellar metallicity. It is not yet clearly established whether the metallicity - planet frequency correlation observed in dwarfs also holds for giants, though the apparent increase in RV noise for low-metallicity giants must bias these studies.