The other thing I don't do is manually set my difficulty. I noticed others here are doing that, but is it necessary? My rigs range from about 800 MH/s to 1.8 GH/s.
You are the third one in a row, if you read the last 3 pages. This problem is caused by the fact that BitParking sets the default difficulty to 16, which is too high for GPU/FPGA mining. You should use "d=1" or "d=2" as your password to set the difficulty lower. This will avoid inactivity timeouts and stratum disconnections.