2004 GMC Sierra 1500 Q&A

2004 GMC Sierra 1500 Question: no heat in 3 of 4 vents speedometer off by 50 miles over

heat defrost work only on passinger side.Recently went out of right passinger side only in middle.Thought it might be heater door actuator.I will admit I mixed anti-freeze this summer. SPEEDOMEETER went wacky 2 days ago at first 20 miles over now 50 miles over,even at rest and shut off thank you, I checked most of the fuses -
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