fishtal,
If your RO/DI is 4 TDS, you need to replace the DI resin.
If your system is running at the normal 4:1 waste ratio and your waste TDS is 370 then your tap water TDS is probably in the 300 range and your RO only TDS should be between 6 and 12. If you are getting 4 out of the DI, it is exhausted and is not doing much for you. It will soon be higher than the RO only TDS as it has started to release all the contaminants it has trapped.