Moving this discussion to the Premiere Elements forum.
A few ways to go on this.
What computer operating system is Premiere Elements 11 tryout running on, including 32 or 64 bit?
What are the pixel dimensions of the photos in the slideshow and how many of them are there?
When you are playing back the Timeline content in the Edit Mode monitor are you looking at the rendered or unrendered content.
Explanation...is there an orange line over the Timeline content during the playback? If so,
a. press the Render button
b. hit the Enter Key of the computer main keyboard
c. go to Timeline Menu/Render Work Area
After this Timeline rendering is completed, what does the playback then look like when there is now a green line over its content and how does it perform?
Is your computer optimized..how much installed and available RAM and free hard drive space?
Did you have your antivirus and firewalls turned off during the download and install of the program?
When you get the freezes during playback preview, what is the duration of that Timeline?
Let us start here and then decide what next.