The Wikipedia article Dutch Railnut linked to is a good start on information about this locomotive model. Of the internet links given at the bottom of that article, one is a roster that will give an answer to the question of which Class I railroads bought them. There is also a reference to a two-part article in the (dead-tree format) magazine "Extra 2200 South" from the 1970s: if you can obtain these, they are a source of LOTS of information (including information on the "phases," or design variants, built over the decade and a half of GE 44-tonner production. (I have copies, and will consult them to answer specific questions.)
Random factoids:
The Pennsylvania had the largest fleet… and regretted it: they discovered, after buying them, that they weren't powerful enough to replace the steam switchers they planned to replace with them. The New Haven, I think, had the second largest fleet: at least one of theirs was, I think, transferred to the Connecticut Company, the New Haven's trolley-line subsidiary, and used for switching in part of street trackage. And, if you are in Australia, one of the 44-tonners taken there during WW II by the U.S. military and transferred to Australian railways has been preserved, in a railway museum in Adelaide.
