Its simple. Check to see if you installed toliet right by removing top of tank and holding handle all the way down. Did it flush from all rim holes? If not, then u will need to get a garden hose with a sprayer to increase pressure and shot high volocity water at rim holes to unblock it. Remember the very front on newer blows do not have holes its a pee shield. Also try doing these other things adjust screw inside tank to make sure the bowl has enough water in it to do a good job. Check the rubber tube going into the hollow pipe and make sure it is going fully inside the plastic pipe that is sticking out of the top of the water in the tank. Also you need to have enough water in tank to allow it to flush good. To increase tank water levels then just unscrew the big plastic ball (or just bend wire to allow more water or bend to allow less water) at top of water in tank. Also increase (max) water pressure at wall to allow it to work at its best. If you have hard water it can cause problems but you say it happened even new, so, you do not have to go in that direction.