Ro/di problems driving me crazy

[Timbits]

I have a 75 GPD aqua fx unit. Usually takes about 8 hrs to make approx 25 gallons. Lately it's been taking longer around 10 hrs so I thought my filters needed changing So I changed the sediment and carbon but production stayed the same. Argh so then I notice my membrane needed changing so I thought it must be that. So I change my membrane with a 100 GPD membrane and replaced with a 100 GPD flow restrictor. Ran the unit again and production rate is still the same! I didn't change my di cartridge because it looks good still and its only 4 months old. But I really don't know what's wrong should I change the di? This is driving me crazy I don't know what to do.

Anyone have any ideas pleaseeeeeee thank you