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+ psi, Water/Meth, 2800 stall, LT headers, Drag radials, Drag alignment, Cradle Bushings. Tuned by Ted.