There's no way you should be losing air in the A3 wheel is every thing is clean. I would first check your new stem to be sure the size of the stem was the correct size for the wheel. Standard over the road (OTR) rig stuff is too small at the stem hole for the A3's and you may have to switch over to an Ag stem like I did. CLEAN the wheels well where the O-rings goes. Clean the beads well and clean the tires well. I've had A3 wheels with used Conti's on for several years with no problems whatsoever.
Here's another trick I used on a different manufacturers less than machined well design as it kept leaking down. I cleaned and painted where the wheel halves met for the O-ring. Then I cleaned and painted the beads. Then I put the O-ring in and put layed a nice fat bead of black RTV around it. I put the tire on without the beadlock insert as I didn't need them and bolted the wheel halves together. THEN, before inflating the tire, take SLIME (found at Tractor Supply used for tire punctures) and pour that around the beads on both sides. Pump up tire, wash off slime, good to go! Don't forget to not be bashful using the slime. Lay the tire down so the bead falls down a little and pour it on there nice and thick, then do the same to the other side. Do not waste your time using slime through the valve stem and hoping it will seal the bead. It won't. Break it down, clean it, then baste the ring with silicon and beads with SLIME.