The instalment will make fun of reality shows such as The Bachelorette, TV Line reports.
Sloane will star as Melinda, the participant on dating show Missed Connections, which sees her having to pick a partner from various men from her past.
When one of the contestants is attacked, Shawn (James Roday) suspects Grunberg's character Dimitri, the show's producer.
The episode will also feature an appearance from WWE star Mike 'The Miz' Mizanin, who will play one of the show's contestants, Mario.
Sloane has recently appeared in Weeds as Maxeen and has also had roles in shows including Sabrina The Teenage Witch, How I Met Your Mother, Mr Sunshine and Children's Hospital. Her movie credits include Bring It On, She's Out Of My League and Horrible Bosses.
Meanwhile, Grunberg has worked on shows such as Alias, Heroes and Love Bites, which was recently dropped by NBC.
Other guest stars who will appear in the sixth season of Psych include Danny Glover, Michael Trucco, Jason Priestley and Jennifer Finnigan.
The show is expected to return with new episodes on USA in October.
Watch a clip from the fifth season finale of Psych below: