Yeah, the SD90MAC and the GE AC6000 were the modern 6000HP units. Both are no longer in production in the US due to Tier 2 restrictions. Both of which have had bad reliability problems. Both manufacturers seem to have problems with the engines failing...CSX has derated all but a few (may be all now) of their AC6000's to 4400HP and designated them C44-6. UP has also had nothing but problems with EMD's H engine in the SD90.
Back in the early 70's however, I do think that one model of EMD's double diesel (DD) line was something like 6200 or 6400 HP. I'm not knowledgeable when it comes to DD40's and all...so I'll let someone else elaborate.
MP 6.7 - Nelson Bennett on the BNSF Seattle Sub
Canon 7D, 20D, 10-22 F/3.5-4.5, 24-70 F/2.8L, 70-200 F/2.8L IS