You may want to try MRIcroGL (you can optimize the "Maximum Texture Size" for your graphics card in the preferences). You did not say what operating system you are using, but in general MRIcron on Linux and MacOS should handle 2gb (decompressed) images. If your image is compressed (.nii.gz) you may want to decompress it, as the original GZip format had a maximum size of 2Gb uncompressed and not all implementations support larger sizes.