Hello, and welcome to Justanswer.
The bad speedometer can be a couple of things. First you have to find out if it is the actual speedometer or the computer, or the speed sensors. If it is a bad speedometer in the Insturment cluster, then the only fix is to replace the cluster.
The temp guage not working could be the guage in the cluster or a temp sensor located on the engine.
The easiest way to determine what the problem is, is to have a shop or someone with a scan tool, performe a guage sweep to see if the guage will move.
Most likely, you have a faulty insturment panel cluster, and you will have to replace it and have it programmed. The theft system works through the cluster.
Hope this helps.
Not usually, most of the time when clusters go out, you will have multiple problems. I just think that it is better to know what is wrong than to guess that it is all in the cluster. I do not like to tell anyone that a cluster will fix all of your problems and then after the cluster is installed they still have problems with one of the gages not working. Hope this helps.
If this answer helped, please click the accept button. Any bonuses are appreciated.
It is not hard to install a new cluster. You will have to remove the trim panel from arount the cluster, which can be a little tricky. Try not to break it. After the trim panel is removed, there will be four 7mm screws that hold the cluster in place. Remove the screws and pull the cluster out. Disconnect the two connectors and then follow the steps backwards to install a new cluster. The problem you will run into is that the cluster will have to be programmed to your vehicle with a scan tool (we use a GM Tech 2). The clusters usually cost between $300-450 plus instillation which at a dealer is about $150-200. Hope that I helped you.