Your findings are what I usually hear and see on top mount setups. If you were to pulley it for 12 psi id bet you would see 160 degrees too.
2011 SS IOM Vert. ECS Vortech 13.5 psi, Water/Meth, 125 shot, 2800 stall, LT headers, Zex 125 shot, Drag radials, Drag alignment. Details in Garage. I hack it up, Ted tunes it in.