After touchdown the only hydraulic systems that should be in use are ground spoilers and brakes. (I don't think 737-300's have hydraulic thrust reversers).
You have one electric and one engine driven pump for each system. That should be plenty of muscle for brakes and spoilers.
You could have a bypassing spoiler or brake actuator.
Measure brake temp with a
. Are they equal temps? Raise the spoilers, is there one not coming up?
The crews shouldn't be pulling up flaps/slats until on taxiway. Make sure they are not.