This is not surprising. Consider that you are running two filaments (100W)in the capsule which normally handles one (50W). So the filaments are going to run hotter (maybe 20%?) and fail sooner. You really need two separate halogen capsules (see sig) but it will be expensive.
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1997 4x4 CC 5spd, CPL1553 pump, Horton fan, Sport headlamps, Optima RedTops, 98 shift levers and console, RS5000 shocks, Yaesu VHF radio, and BCT7 scanner in the overhead console... N7DAL.