I just bought a T20 and have been testing it in route mode while attempting to apply a rate of 2 gallons per acre (GPA).  I initially calibrated the pumps and flow meter and began to spray.  Everything works ok except the rate is consistently 15-20% off.  I put in 5 gallons and it empties the tank but the system tells me it applied 4.1 gallons.  I could deal with the rate discrepancy if I could adjust the dosage rate in small increments but when I attempt to change rate with the slider on the rc it only moves by 1 GPA.  I need it to adjust in smaller increments like 0.1GPA so that I can achieve my desired rate and I haven't had any success in finding a way to do that.  Any help is appreciated.

Hello my friend!
Have you performed all calibrations related to the spraying system? (Flow meter, pumps, etc) ??
Beside that there is an option (at least at the T30 we have it) that keeps an certain amount of liquid remaining, even while showing "empty tank" message, to avoid trapped air or something like that. Even though 1 gallon seems pretty much for that, usually for T30 we can keep about 1 Liter only.
I have not the RC in hands to confirm it all but We can talk further if you do not figure it out.

Thanks