What happens when you ldd $(which glxgears)? Check the version of libGL.so that it's loading, and make sure that that version points at the nVidia version.
I know you said all libs are correct, but it is possible to miss one or two. That, coupled with the strange search path order of the dynamic linker, can cause problems.
Also check your X log to make sure that libglx.so is loading when the "glx" module gets loaded. If it says libglx.a, then that could be your problem -- libglx.a is the standard X glx, not the nVidia glx. Move it to either another directory or another filename (like XXXlibglx.a or something) and try restarting X.