My 1993 GMC Sonoma pickup's gauges recently have been jumping by themselves while driving. The speedometer will jump to different speeds while the vehicle is at the same speed, and the fuel gauge will rise and fall drastically, while driving. The in tank fuel pump and sending unit were just replaced about 4K miles ago and worked fine when installed. Truck also pings when going up hills. Timing was checked, and is fine. I am thinking maybe it could be the PCM going bad and causing false signals. Anyone have any ideas?
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