I’m a diy’er who built my “M370” from an 350HR manifold. The difference you and I felt is documented in the Motordyne post below. The boost in power that occurs at rpm’s below the 7300 rpm shift point of the 7AT really helps 7AT performance. Also using the engine at lower revs reduces oil pump and valve train wear and tear.
http://www.the370z.com/intake-exhaus...tml#post819715