Based on what I can tell, the Y origin of your intended domain is not offset by an integer multiple of 4 km from the Y origin of the 4 km gridding surrogates:
4 km gridding surrogates header:
#GRID us4k_1548x1332 -2952000.000000 -2772000.000000 4000.000000 4000.000000 1548 1332
Your intended domain:
‘LAM_40N97W’, -1848000., -842000., 4.D3, 4.D3, 50, 50, 1
x offset of intended domain relative to gridding surrogates in terms of grid cells: (2,952,000 - 1,848,000) / 4,000 = 276
y offset of intended domain relative to gridding surrogates in terms of grid cells: (2,772,000 - 842,000) / 4,000 = 482.5