2005 chevy trailblazer
 

my gas tank light always says im empty when i fill the tank and my speedomoter also tells me im doing 100mphthen it gos to 0mph HELP!!!

Bad computer juju. For best results, take it to the dealer.

Gm has had a ton of problems with the instrument clusters on their vehicles, especially trucks and SUVs in recent years. The instrument cluster is about 99.999% likely to be the cause of your speedometer problem and may also be causing your fuel gauge problem, although they have had a lot of problems with the fuel level sender in the gas tank as well. But I would get the instrument cluster fixed first. If it is out of warranty then the cost of an exchange or repaired cluster is generally around $300-400 for the part, and about 2 to 2.5 hours of labor to replace the cluster, and program the cluster if necessary.

Thanks man!! If you need any advice on plumbing ? give me a shout! union plumber!!!

Ya it's allways something with you kanucks

I'm betting on 2 separate problems---cluster & pump. The sending unit and pump are 1 module on these vehicles, lots of $$ if not under warranty. The next time the speedo acts up, try pushing hard on it to see if that makes it do anything. If you're lucky it may just be the connection at the back of the cluster, or possibly a bad speed sensor. Go by Autozone or some such and get a free scan for trouble codes. No codes, you can rule out a sensor. I would just learn to live with the tank level being off and keeping track of the miles per tank using the trip meter. Good luck.