Exactly, Scotty was just about spot on. I believe 1984 was the last of the remaining black "PC" units from the families of SD40, GP35, GP38, GP9, & RS3. By 1980/81, just about all first generation stuff was sold, traded in, retired or mothballed for traffic surges. This included alot of worn out U25B, U28B, U33B, C630, C425, RS3's, GP7/9, NW2, SW1, SW7/8. A few dozen GP7 & GP9's were rebuilt buy IC Paducah shops with a chopped down high hood, and others into GP10 high hood.
1979-1984
Most Typical engines for Road Freights:
SD35, SD40, SD45, SD38-2, SD40-2, C30-7, U33C, U36C
GP38, GP40, GP40-2, B36-7, GP38-2, B23-7, (occasional U30B, U33B, U36B, GP30, GP35)
Branchline Local Switching, and light industrial work:
GP38, GP38-2, B23-7, U23B, SW1500, GP15-1 (occasional GP7m/8/9/10, GP20, GP35)
Yard Mules & Slugs:
SW1500, MP15, MT-6, MT-4 (occasional SW8/800/900, GP20)
1984-1989
Most Typical engines for Road Freights:
SD40-2, SD45-2, SD50, C30-7/a, C36-7 (occasional SD40)
GP40-2, B36-7, GP38-2, B23-7 (occasional GP38/40)
Branchline Local Switching, and light industrial work:
GP38-2, B23-7, SW1500, U23B, GP15-1 (occasional GP10, GP38, GP40)
Yard Mules & Slugs:
SW1500, MP15, GP10, MT-6
In addition to Railpace magazines and Conrail's own magazine “Update”, I had the privilege of listening to the scanner in my bedroom while I did my homework after school. Just the mention of unit numbers on the radio told me what was roaming the rails and where, and how frequently. Then of course, I spent many of my summers along the CR Mainline between Rochester & Lyons around 1980, up until my last years of High School in 1990. Then I went to Buffalo for my engineering degree at UB, where I found GP10's mated with slugs were common doing yard work and local transfers for several years into early '90's. I believe the GP20's were commonly used with a slug for the hump at Syracuse until about '82 or so. A pair of SW1500's were commonly used on locals in Rochester (to Kodak on WBRO-26 or to RG&E on WBRO-16). Sometime in the late '80's, a magazine showed a picture of a Conrail GP30 doing a local turn out of Philly or the Jersey area. But that was a rare situation when a power shortage came up, and a few mothballed GP30's and GP35's were briefly brought back from retirement.