Check the propane tank to make sure that it is full. A near empty tank can cause this problem. Try using a full tank and see if the burners work properly.
If you have not cleaned the burners recently, I recommend that you clean the burners according to the guidelines in your owner's manual on page 19. Make sure that the orifice is clear on all of the burners.
Here is a link for the owner's manual in case you need it:
A bad regulator could cause the problem if the above tips do not help. You can try replacing the regulator (part P03601001A is a regulator and hose assembly). This may fix your problem.
If these tips don't help, then you will likely need to have the grill serviced by a technician. Here is a link for the Sears Service website:
Sears Home Services
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