On my 1999 chevy silverado the only gauges that work are the oil pressure gauge and the temperature gauge. nothing else is working cot even the speedometer or the RPM gauge.

If all the gauges on your 2008 Chevy Tahoe have stopped working, it is possible that there may be an issue with the instrument cluster itself. A malfunctioning instrument cluster can cause the gauges to stop working all at once. Other potential causes could be faulty wiring, a blown fuse, or a defective sensor. I would recommend taking your vehicle to a qualified mechanic or dealership to have it diagnosed and repaired.

Because revving the motor makes the oil pump spin faster and therefore increases pressure. It should be stable and within specs when you are at cruising speed.

check the filter,, if its bad enough your oil won't pass through it, making it look like your oil is full, but its not moving, Chevy's have whats known as a stepper motor also on the oil gauge,, whats bad about that is if thats gone bad, you have to replace the whole gauge cluster which last time I checked is 250.00

It could be the sending unit. If the truck is low on oil it will cause something similar. Be sure the oil level is topped up. The only way to be sure it so measure the actual oil pressure at the engine with a proper gauge..

you should switch the temperature sensor and oil pressure sensor you had on your first engine,because your new engine must come with the light indicator dashboard so the sensor of your new engine are not compatible with your gauges....lipak!...

yes new cluster, these truck are notorious for that i just replaced mine they have to be programmed to your vin and mileage to work the right way

The stepping motors in the gauge go bad, but uusually they fail gradually, or just one, The dealer charges $300 to fix, do a search on ebay for CHEVY SILVERADO INSTRUMENT CLUSTER for cheaper repair options. gauges are powered by the pcm, no fuses inbetween, so if it runs ok, problem is in cluster

The 'check oil pressure' gauge indicates less than 5psi of oil pressure. This usually indicates either a oil pump pick-up screen is plugged up or the crank bearings are worn to the point that oil flow is not being restricted. Both require the removal of the oil pan to check for the problem.

The pressure to be most concerned with is the reading in gear at idle with engine warmed up...Low end really should not be below 20. If pressure wanders, change the sending unit and check actual pressure with a mechanical gauge if necessary. The age and quality of your oil, as well as temperature all play a part in pressure, as well as internal wear from time & miles of use. If pressure changes with rpm, that is normal. 40psi is good while driving.
need more info just ask.

The fuel pump on that model runs through the oil pressure switch so that if the truck looses oil pressure,It kills power to the fuel pump to prevent engine damage.you need to find the cause of the low oil pressure reading(possibly a bad oil switch).That would be the cheapest place to start,or have it checked with a mechanical gauge.Good luck,
ChevRev