I purchased a 60 gal Ingersoll Rand SS5L5 compressor from my local tractor supply a few yrs back. After having it a month I have had the same problem when filling the compressor and it cycles to about 40 psi it slowes the pump down to where the electric motor actually burns the belt for a few seconds then it speeds up and fills to where it shuts off. I have went round and round with Ingersoll and changed the belt a few times and it still did the same thing. The second time I contacted Ingersoll the sent me a whole new pump it did not fix the problem. They told me if they sent a tech from Atlanta and if the problem I had was not fixed under warranty they would charge me $650.00 for the tech's time. I am now out of warranty and am trying to fix the problem my self. When I turn the air compressor on and it starts to slow during cycle I can pull the release valve on the check valve and the compressor speeds back up almost to normal operation. I replaced the check valve and it still does the same thing. I have unhooked the tube coming from the pump to the tank and the compressor pumps normal. Its almost like something blocking the air to the tank or the pump is fighting against the pressure from the tank. I am at a stand still and don't know where to go from here. Any help will greatly appreciated!