Hi,
tex3DGrad() or texCubemapLod() could be the CUDA function you are looking for.
(in CUDA C Programming Guide https://docs.nvidia.com/pdf/CUDA_C_Programming_Guide.pdf)
maybe also take a look at my question: tex2D in OptiX7
in an existing app which uses a version earlier than OptiX 7.0.0 it was rtTex3DGrad
or rtTexCubemapLod :
https://raytracing-docs.nvidia.com/optix/api/html/group__rt_tex.html