I have an 07 Tahoe I'm having problems with my driver side power running board. It folds down fine when I open the door but when I close the door it struggles to fold up. What could be the reason?

Are you in cold country? You may have gunk frozen and it will not run as fast as it is being hold up. If it is warm, check to make sure there are no obstacles preventing free movement. A bearing may be going bad since it is nearly seven years old. This also will slow it down as it struggles to move. The motor may be failing. Are the wires connections clean and deposit free? Sorry, but you must get a bit dirty and crawl under the truck to inspect if you don't have a lift to check it. My first guess is there is something preventing free movement. Has it been damaged so it is out of alignment? Perhaps dirt, snow, or other foreign object like opossums are in the mechanism.