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?
Posted using the http://www.autoforumz.com interface, at author's request
Articles individually checked for conformance to usenet standards
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.