general problems of the 2005 Buick Lesabre

The first incident was around 40,000 miles. The gas guage would not work, after filling it up the guage would "stick" or the hand would drop down to the thermostat needle. Very irratic. Carried it to the dealer and naturally, everyyhing appeared to be working. 52,000 miles and the guage is dead - of course the warranty was out also. It was explained that I would have to replace the entire cluster of guages and I could not afford that at the time. Car now has 79,000 miles, I have been using the oddometer so I will know when I need gas. A few weeks ago, looked at the speedometer and it read my speed as 120 mph. I immediately pulled over and at a dead stop, the speedometer was setting on 60 mph. Now I am concerned about the entire cluster readings. The thermostat will jump up to the red, hot reading which is wrong. Now I am going to be out huge dollars that appears to be something gm should repair.