So what is your recovery rate in liters/hr?
math
3.75 x 30 / 9 ==> ~ 6.25liters/hr on each
Maybe you need the New summit research max rotovap 80 LPH!?!?!?
I think we finally got the FFE supporting four 840mm fuges into the 650l/hr range we need in the last month or so. It required tweaking ALL the things we could modify.
Can you list what those things were?
In order to solve this, you need to know them.
I suspect the open source FFE thread will list them all.