Tachometer and Speedometer Not Working

I know very little about vehicles. My question, is at times my tachometer and
speedometer will not work on a 1996 GMC Yukon 4x4. It does this periodically
and with, I think, no consistency to weather as I live in the cold northeast.
The worst part of my concern is when this does happen the vehicle takes about
5-10 seconds to get up to speed with the throttle pushed down approximately
halfway to more. Even then the truck stays in third gear at/around 2200 RPM's.
I am hoping to get some sound advice before taking it to a mechanic. Any help
is greatly appreciated, thanks in advance.

>I know very little about vehicles. My question, is at times my tachometer
>and
> speedometer will not work on a 1996 GMC Yukon 4x4. It does this
> periodically
> and with, I think, no consistency to weather as I live in the cold
> northeast.
> The worst part of my concern is when this does happen the vehicle takes
> about
> 5-10 seconds to get up to speed with the throttle pushed down
> approximately
> halfway to more. Even then the truck stays in third gear at/around 2200
> RPM's.
> I am hoping to get some sound advice before taking it to a mechanic. Any
> help
> is greatly appreciated, thanks in advance.

Does the speedometer ever read incorrectly or does it just flat line?

When does the speedometer stop working? Doesn't work at all when you start
the vehicle? After you've driven for a while? What about the tach?

Does it not work when the vehicle is cold or after you've done a few trips?

How old is your battery?

Steve