Sealand was owned by CSX. With the breakup of Conrail, and the new crossover installed at CP-5, NYS&W was cut out of hauling this traffic. They still do the switching of the yard though. Sealand does no exist as an independent anymore, having been sold to Maersk, ergo Maersk Sealand.
The Hyunadai and other stack traffic went to NS, which also happened when the contracts ran out within a year or two of the CR split.
The last transcon traffic to go was the autorack train, which also went to CSX.
I believe these were the main reasons Mr. Rich had NS and CSX buy into the company. Their assimilation of CR doomed the NYS&W's long distance traffic.
Also, there was a post on the NY forum from Idiot Railfan that an NS inspection train (probably the GEO train) ran the Tier between Binghamton and Port Jervis and that hints were made that it is in anticipation of sending intermodal freight down that line. One can only hope.
Just as a follow up I saw the SU-99 last night. He went west through Butler at 8:50 pm. Reported clear of Sparta at 9:50pm. Two engines and 21 cars doing track speed. So that confirms the 50-60 minutes between those two points.