We use Dataease 6.53 on three PCs. One who works as a server and workstations, and two who are satellite workstations. This two are so slow when doing a search. It can help with a restart, but after a day it becomes slow again. It has been so for a couple of years while I thought the PC was the problem. But now we have change all three PCs and the problem remains. 
"Locking strategy" is set to "Full"

Best regards
Sondre Grinna

As a first attempt I would try to set the locking options to opportunistic. 

Locking in itself is a database so it makes sense to limit traffic as much as possible.

When you are running an application alone on a network it will know its alone and skip a lot of the disk activity needed to "play nice" with other users. This is why it goes slower when two or more users use the system at the same time.

So a quick server and a good network is paramount in getting the best result. 

The client computer is almost always powerful enough to run any DataEase application so the problem is the server side of things.

Image your server as a slow hard-drive and you get the picture. The more you need to read/write the longer it will take and when you share files the management of that is more labour intensive than the reading/writing of the data itself.

So the solution is to turn your server/network - it is the combination that matter in the end as nothing is stronger than the weakest link - into a fast hard-drive.