problems with my shurflow trailking 7 pump?

Hi I am having problems with my shurflow trail king 7 water pump in my motorhome, when I operate the hot water tap the pump takes several minutes to kick in, when I turn off the hot water tap the pump continues to run for several seconds after. The same is happening with the cold water tap but the pump kicks in quicker and shuts off quicker. I have drained the water system and reprimed the whole unit several time to no avail, I have also removed the strainer and plumbed direct into the motor in case there is a crack in the strainer but again to no avail. I have read several forums and can not find a reason why this is happening, we have lived in the van for 3 years and have not had any problems with the pump to date. Oh another thing the water pressure coming from the tap seems to be a little lower than usual. Hope you can help.