Stalling in Overdrive

My son's 96 Bonneville, now stalls in Overdrive when stopped at lights. More or less a nuisance problem. Although we just had the transmission rebuilt, and the transmission guy thinks the throttle needs adjusting, which of course he doesn't do. Hate to bring it somewhere else. My son is driving in Drive, and that seems to be fine. what is the preferred gear to drive in OD or Drive?