GP38-2s and U23Bs would probably be the last PC power (both had 1973 delivery dates). I think the U23B's were actually the last delivered (October 1973 build vs. March 1973 for the GP38-2s), but the information I found might not be complete. Based on numbering, it appears that for 6-axle EMDs, SD40s came first, followed by SD45s, then another round of SD40s (I suspect the '45s were original PRR units or units that were ordered by PRR pre-merger and delivered post-merger, with the second batch of SD40s being the PC orders). No Dash-2 6 axles on PC's roster.
http://www.trainweb.org/nycrail/pc/pc2.htm
http://www.locophotos.com/Roster.php?RoadID=311&=
GE, not EMD, makes the best locomotives now; has for over 30 years. Get over it.