Myssdragn's post is similar to our '05 Georgie Boy, with the exception that the bedroom slide motor is under the foot of the bed on the side toward to the back of the motorhome.
If your batteries are running low, that will cause the main slide to struggle. If you start the engine, that should help. That's actually how I know it's time for new batteries.
You should have a slide controller somewhere. On my rig it's behind the main breaker panel. The controller houses the relays and control logic so that the slides operate when they should.
Assuming your slide motors have electric brakes on them, the "Manual" button next to the Slide In/Out switch needs to be pressed IF you try to crank them in manually. This button releases the brake on the slide.
I had an issue on our slide in which it appeared that the brake wasn't being released by the control module when the slide was going in and out, so the slide was really struggling. I did a bit of rewiring (Wired the brake to the motor power so the brake would release anytime when the motor was on (like it's supposed to)) and that fixed the problem.
Lastly, make sure all of the power and ground wires on the motors and the controller are clean and tight. I noticed one of the ground wires on the controller module was loose and the insulation was burnt about 6" up from the chassis ground connection. When I fixed that, the slides started working much better.
Yes, I have had a couple of issues with the slides on our GBM. Most were due to poor installation practices.