1995 LT-1 speedometer slow

Problem with my 1995 LT-1 My speedometer is 7 to 8 MPN slow when it shows 55 I am doing 47 to 48. My Temp Gauge is also showing high a 40 degrees shows 260 temp is 220. I have replaced the computer in dash
and under hood and all relays. What can be causing this problem?
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