2002 Prius MPG Readout failure

I have a 2002 Prius. 135K miles on it. Recently the dashboard display had the trouble light on. I noticed that the cruise control was not engaging. Later that day, I filled up the tank, pressed the RESET button on the FUEL CONSUMPTION SCREEN, and the MPG and Mile Counter went to O. The mile counter and the MPG remained in O for several hundred miles until I took it to the dealer.

They ran a "A complete system analysis" and found "an open circuit with the instrument cluster". They replaced the cluster (part #83801-47031-RP). Both numbers were in 0.0 when I drove out of the dealership. I noticed immediately that the MPG readout stayed in 0.0 for most of the 2 miles that took me to bring it back to the dealer. I couldn't leave it that day, and have been driving it for about two days and 200 miles. They fixed the cruise control; the mile counter on the screen is working too. BUT the MPG has been moving upwards very slowly from 0.0, up to about 22.2MPG after 200 miles. Any ideas?