When I start my 2004 envoy xuv the oil pressure is almost zero, I turn the car off and restart and the oil pressure is fine then any Idea whats wrong

It's a short in the instrument cluster.
I had the same problem with my 2004 XUV.
It started in early December of 2007.
Intermittent manifestations, than more persistent.
Took it to the GMC Dealer --
Of course, the Truck wouldn't do it's tricks for the Tech.
They replaced the ignition switch and sent me home.
It got progressively worse.
I waited until I was sure it would do it for the tech.
Took it back in to GMC Dealer--
It's a short in the instrument cluster.
They needed to replace the entire cluster.
I bought an extended warranty when I bought the truck.
The warranty is still in effect --
So I only had to pay the $100 deductible.
No Idea what it might cost otherwise.

The video will show you.
How to GMC Envoy Bose car Stereo radio Removal 2002 2005 replace repair

probably the fuel pump . could also be the coil . no idea the yr what it was doing any problems the day before ???

this is the exploded view of tailgate https://www.gmpartscenter.net/v-2004-gmc-envoy-xuv--sle--4-2l-l6-gas/body--tailgate this is removal and working on an xuv https://www.youtube.com/watch?v=MLQLAD8xOPk

Sounds like the power steering pump has seized up. The question of whether you can change it yourself depends on your abilities and knowledge of auto mechanics, and having the necessary tools.

Oil was check with a dipstick?then you only check its volume,here the real check you lost pressure.The oil pump supplies oil to valves to timing chain but is not the device that creates pressure, pressure is created by the cranksahft and its main bearing, if the oil pump fails then the crankshaft cannot create the needed pressure ,is the pan hit? Do not turn this on no more, youll need to get it inspected, if you run ir it will just freeze up. tow it to a repair area,

2004 Envoy xuv 6 cyl when I turn on the A/C the truck stalls but as long as I keep my foot on the gas it will continue to run

More than likely the throttle body needs cleaning

i would say it's long overdue. i would think the manufacturer would recomend changing the trans fluid at 25,000-30,000 miles. the owners manual will have regularly scheduled maintenance routines listed.

You need to replace the oil pressure sending unit, this is what tells your gauge what the pressure is. For future information if your oil pressure drops again and its a real failed oil pump within a few minutes you will internally damage the engine. I would get a new Oil Pressure Sending Unit. Let me know if you have any questions.... Thanks!