Kubota b7800 does reach 540 RPM at full throttle

Let check is it helpful or not?

The redline torque of the Kubota engine is where the engine pulls weakest, producing only a total of 37 foot-pounds when the throttle is opened to the full 3,600 rpm maximum.

Peak torque of the Kubota arrives earlier at 2,400 rpm on the tachometer, producing a total of 41 foot-pounds, along with 19.5 horsepower at the time.

Have you ever heard of RPM roll over? If the engine was allowed to reach it's max RPM under throttle the inertia would cause it to exceed its design max RPM, so it set below that to avoid flying rods and pistons. And yes it is governed.

You just go to the link I attached I'm sure you will get the solution of your problem -

https://www.reliable-store.com/products/kubota-l185-l235-l245-l275-l285-l295-l305-l345-l355-tractor-service-repair-workshop-manual-download

Would check ignition switch, maybe you can just spray liberally with electric contact cleaner in every opening you can find and then blow out with compressed air before it dries.

the specifications for the tractor show a transmission int-shift 24f/24r/(32f/32r) option with creep
creep speed is ( casset e type is listed at optional(.19-.74km/h)
.74 km/h = .459 miles /hr
the specs show that the pto speed is 500 rpms /1000rpms ( interchangable rpm)
reference www.kubota .com.au or m110gx-kubota tractor coorporation
you will have to talk with the service dealer technicians as from the specifications , what you want is available as an option
if not and you are using some sort of seeding machine , it may be an option to change the gearing in that machine to achieve the same results

hydraulic pump dead

you do mean a 100 rpm pto up to a 540 rpm pto correct ?

tractors that have the wrong rpm are difficult to speed up as your going to have to give up shaft power (Horsepower) to do this so if your implement is already drawing your hP down , adding a speed increaser is going to make things worse

some out of the "normal" box things ive seen folks using the belly mower take off instead of rear pto , belly mower take off's are sometimes a higher speed but again have less power than rear pto points

Visit the on-line store, known as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem -

https://www.reliable-store.com/products/kubota-b2630-tractor-workshop-service-repair-manual

Just Had the same thing happen to my B7800. Turns out it was a sticky PTO safety switch. I manually activated the switch a few times problem solved. If it happens again, guess I will replace the safety PTO switch.