Not all the specifics of the PRR's last steam operation are available, but we can come close; the last revenue run was a loaded coal move from Cresson to Altoona in late 1957, using I-1 power. According to the memories of some who were "on the scene" that move came on the day President Eisenhower suffered a mild stroke, which would have been November 25.
Two days later K-4 No. 520 powered a Baltimore-Northumberland steam excusion; however, this would not qualify as revenue service in the strictest sense of the word.
The link below shows a photo of an I-1 in switching duty at Harrisburg; it's dated Nov. 30, 1957. The authenticity can't be confirmed, but the completely bare tree in the foreground argues in its favor.
http://www.railpictures.net/viewphoto.p ... showexif=1
I'm in agreement with the earlier post on N&W's "official" termination of steam in early May of 1960, but according to some locals, a few of the Y-6b's may have remained in service between Grundy and Ieager a while longer.
Grand Trunk also operated steam into 1960 in southeastern Michigan based in Durand. The last official passenger run (from Detroit) is listed as March 27, but records of service in other capacities are sketchy.