Getting some freezing drizzle in CO this AM and I've got problems. The heater/defroster isn't putting out consistant hot air. Driving through town it didn't seem to warm up at all. Got on the freeway and it heated up. then back to surface streets and got alternating cold and hot air. The blower speed is fine -- replaced the FSR last year to fix that issue. Diagnosis?

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2001 X5 3.0i