PTO speed has no dependence on what gear you are in , it's only dependent on RPM of the motor.
Are you saying the Tach does not work?
PTO operation is 540@2295RPM
Max rated RPM is 2600RPM
so guess at a little less than max RPM.
Now as far as your problems with anything on that tractor, you need to understand the M7040 has been in production for longer than any other model that I can think of, and it has 20 Sub models, so saying you have an issue with your M7040 is like saying you have an issue with your Chevy.
If you don't know the exact model designation, post your serial # and we should be able to figure it out for you.
Here are the models' and don't just guess!