3000sqft in western canada. 4.5 tons combined capacity might still be on the big side. You should have seen some improvement however. But as mentioned, a 3 ton coil with a 1.5 ton condenser will result in a dry coil unless you really, really slow that blower down. I think a 2 ton coil is about as large as you want to go. I'd start by slowing the blower, but long term
you may need to put in a properly sized, matching air handler.
Also, 6CPH as mentioned is way too much. 2-3CPH is better for AC.
Thanks Motoguy (and everyone else taking the time to try and help). The 3T unit has a properly sized 3T condenser (I'm told). The 1.5T unit is new (Rheem) and I saw them install a new Rheem condenser. I'd be shocked if they mis sized it again. This is a bit maddening. Outdoor air temp is 23C today. At my office, when I arrived, indoor air temp is 23C/RH = 38%. When I left home the house was 22.5C/RH=59%. Both systems were cooling to the same exterior conditions and I used the same hygrometer to take the measurements. Not a professional tool though - a $20.00 unit from Home Depot.