From my days in HAM radio and TV antenna installation, 75 CM Band (440-480 MHZ) and TV UHF channel 20 (512 MHZ) were the highest frequencies to use RG59U. Too much loss above those, so Way too much loss for use between the LNB and the satellite receiver. It will work fine between the satellite receiver and the TV on channel 3 or 4 (VHF).
In SeaTac, a 50 foot run of RG59U would get Ch.20 fine but not Ch.42, while an uncut 100 foot piece of RG6 got both very well. So, I also am surprised you were able to get anything on RG59.