Issue with DAF DB250 ALX400 Bus 2003

[HHBOps]

Hi folks, I am wondering if there is anyone around who could perhaps help.

We use the bus for a tour, but it seems to have an intermittent problem where it seems to jump out of gear, revs a bit higher and goes in to limp mode and crawls along at 3mph. It does clear after a quick recycle but does it again sporadically.

I have changed the gear box oil and changed the filter, reset the battery as per instruction but this does not seem to have made any difference.

Is there anyone out there who may be familiar with the mechanics of this type of bus who may be able to point me in the right direction?

Best.