my 2001 ranger 4x4 extended cab wont rev up pass 3000rpm, why

there are several things that might cause that...i would start with a new fuel filter first.....

If the fuel filter doesn't fix it it is likely a plugged catalytic converter(s). You could temporarily unscrew the front O2 sensors and see if the maximum RPM increases or drop the header pipes from the exhaust manifolds to see if that pins down the problem for you. Also a vacuum gauge can easily diagnose plugged cats.

Watch this video for vacuum testing....https://www.youtube.com/watch?v=d-jp1IIJVVk