2000 Pontiac Grand Am oil or sludge in coolant resivoir and

Today I was going to flush my radiator and found a lot of slude or oil in the reservior. My temp stays on about 150 to 160 while draiving @ 60 mph. It will increase to about 195 to 200 at long idle periods, but will drop back down while driving. Also one transmission question. Somtimes it has a slight hesitation the rpm hand with vary back and forth at about 2300 rpm while going uphill sometimes, but not always. I have droped the pan changed the filter and fluid, and noticed no metal shavings in bottom of pan any suggestions. The car runs good does not smoke. Thanks for any help. Also changed fuel filter and air filter, all wires and plugs.