instrument cluster problem

This is a pretty common problem with the 03-06 Silverados. It's caused by a failing gauge motor inside your instrument cluster. It can be rebuilt - check out http://drspeedometer.com/services-i-offer/silverado-speedometer-repair for more info on the problem -V8Turbo

put a used claster in it

the same problem happen to me but there is a guy on ebay that fixes them for cheap and it doesnt take him long and it will be fixed for good but also there is a recall on them if your not over 100k

Common problem with these. They can be repaired here: http://www.mrwhizard.com