My current Intek has pump with SWG built in. Is it possible to buy just the pump connect it in series before the Intel so the SWG would still work.
Probably not. You will probably need to replace all three items (SWG, Filter and Pump). Intex doesn't make it easy to just replace one. You might be able to get just the pump and SWG and put it on the old filter but you might just be better off getting all three.

But your issue could just be due to chemistry. If you have an algae bloom, the filter will clog quickly and the flow rate drops. Fix your chemistry problem first and then consider a new setup.