Check gages light comes on after truck shuts off

check the oil level and the coolant level also not being a smart a.. check how much fuel you have the fuel ---does it restart

Oil sending switch needs replaced.

Check or replace Fuel Filter... have somebody check your idle speed....

I can't speak for the engine light issue, but look into stepper motors for your gauges for the oil pressure issue. I just purchased a used '04 Trailblazer EXT and the tachometer stopped working 1 week after driving it off the lot. I did some looking and apparently the Delphi motors that GM used do not hold up. "Check this link for more info...
http://forums.trailvoy.com/showthread.php?t=48886

Hi!!
If the check engine light came on, drive to the nearest AutoZone, Checkers, or similar autoparts store. Have them scan the vehicles computer for trouble codes,this is a FREE service, you'll get a print out of the codes and a short description of the fault. If you ask the tech to explain the probable cause, most of the time they would do it. If you need further assistance, contact FixYa again.
Good Luck!!

Possible IAC valve or crank sensor. have your vehicle's computer scanned at autozone, its free!! Then post the code on fixya.com, this is the only way we can find the problem. Hopefully this helps

This is very common, in fact GM issued an extended warranty on the gage clusters from 2003-2005. Unfortunately the extended warranty has expired. The cluster either needs to be replaced or rebuilt. I know there are several companies that specialize in rebuilding them, but it takes 3-5 days and the vehicle is not drivable during that time and the repair is not cheap. I just checked and there is one on e-bay for $90 that may work for you. Here is the link, good luck! http://motors.shop.ebay.com/i.html?_nkw=trailblazer+gauge+cluster+&_cqr=true&_nkwusc=trailblazer+gage+cluster&_rdc=1

Check gauge light can come on for a number of different things, from Low fuel to low oil pressure to high engine temperatures. When the light comes on check all the gauge's and see whats causing it, one or more of the gauge's will be showing an issue, Low fuel or low oil pressure, Low battery power. Any of the mentioned things can cause it... Figure out whats causing it then you can remedy the situation...

Check the gages by turning the key's to the run position and see if the gages work. If not check the fuses and then work your way to the wire harness. Good luck

Sounds like the sensor is failing.Have oil pressure checked with a mechanical gage to confirm. A new sensor or wiring repair is allot cheaper then a new engine!!