Wasn't the clearance on the Grand Central west of the BQE raised?
That's a separate issue, and overhead clearance isn't even it - the posted clearance of the 31st St overpass on the highway is 12'6". The posted clearance under the N/W trains on the service road? Also 12'6". Which, since NY posts legal clearances that are a foot less than actual, any truck that is under the usual 13'6" height limit will slip under either.
But yes, 3-axle box trucks are allowed to use that section of the Grand Central now. Larger trucks are still legally required to use the service road to get from the bridge to the BQE. Not because of overhead clearance but because of lingering drama over "it's technicallyyyyy a parkway, sooooo....."
All of this is distinct from the issue of maximum truck
length. Standard US-spec big rigs have 53' trailers. Except for the through routes outlined previously, NYC limits trucks to 55' overall length including the cab, which generally translates to a trailer no longer than 48'.