When i come into a complete stop the oil gauge goes down.

hot or cold engine , or both.?
the oil pressure will be in direct ratio to engine rpm. slow low, fast high
due to the oil pump connection to engine crankshaft.

stalls.: can be caused by 50 things, or just 4 in physics.
the EGR valve (if you have one, no engine stated)
can stick open and stall any engine, and in fact LOVES to. clean it.
1: list 12vdc to EFI. (spark and fuel brain) dash lights dim?
2: lost compression hot, ? compression tests.
3: lost spark, do spark tests. and timing, checks.
4: bad fueling, too much if floods, and misfires and stalls.
too little fuel, it starves and dies.

the 1 free test, is can you save the stall with a fast right foot.

we do the tests. avoiding those 50 guesses....
each tests are simple and the tools dirt cheap .

Did the mechanic drive the truck with a mechanical gauge to check the pressure ? The engine bearings or oil pump could be worn enough to allow pressure to drop at idle after it warms up.

Have you checked the coolant level after you did some driving. Often you will get an air lock in the system which will eventually work its way out after you drive a little. As the sender for the temperature gauge is at the top of the engine, it is possible that it is not fully immersed in coolant and hence is giving bad readings. Topping up the coolant will fix that. Some vehicles can be very hard to purge of air and some even have air bleed points located on the top of the engine as it is the only way to get all the air out.

ur oil sending sensor is bad it reeds the oil pressure

First we would need to know when this occurs. Asuming the oil level is at the full mark!. If the pressure goes up during acceleration and down at idle when engine is fully warmed up, then this is normal. An engine requires 10 psi of oil pressure per 1,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) . If the gauge is moving back and forth erratically at idle , i would say the gauge is bad. If it drops to 0 while accelerating I would say your oil pump is bad. If from time to time it seems to work and other times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. If the pump failed you would start to here a Knocking noise from the engine in a short period of time. Use the above scenario's to narrow down what it may be.

Might just be the sending unit. I've had to replace mine 2 times on my 01. It was located near the oil filter towards the back of the engine. there is a wiring clip and then you need a big socket to unscrew it. Hope this helps.

engine oil pressure may be low remove oil pressure sending unit and install a pressure gauge check for pressure while warm if pressure is ok replace oil pressure sending unit oil pressure at idle should be between 5-15 psi at min

Information taken from: http://www.idavette.net/tech/oilreset.htm

[quote]
The "Change Oil" indicator is reset by using a sequence of Driver Information Center (DIC) key presses as follows:

1. Turn ignition "ON", but do not start engine. (ALDL pin "G" should NOT be grounded.)
2. Press the "ENG/MET" button and release, then, within 5 seconds, press it again.
3. Within 5 seconds of Step 2, press and hold the "GAUGES" button. While the button is held, the "Change Oil" indicator will flash.
4. Continue holding the "GAUGES" button until the "Change Oil" indicator stops flashing and goes out, indicating successful completion of the reset cycle. This should take about 10 seconds.
If it does not successfully reset, turn ignition "OFF" and repeat the procedure from Step 1.
[/quote]

Two things...when it reads zero, is there any engine noise (tapping or knocking)? After you rev the engine does the pressure read normal at idle and function normally, or does it go back down? Either way, you should not drive the vehicle 'till you have a mechanical gauge (yours is electro-mechanical) put on there and the actual pressure is tested. The condition may be a bad sending unit, a bad bearing or possible obstructed oil pump screen. The repair is obviously different for each one and the price is as well.

You need to have a mechanical test gauge hooked up to see if this is a false reading, this special gauge goes into the oil sender tap in the block and will let u know for sure if the pressure is to high cold, if it is the most common issues are wrong weight of oil, do u use oil heavier than 10W-30W? any other oil like 10W-40W will cause high oil pressure readings, the reason is the very tight rod and main bearing clearance's the engines now use, it is only about 1/2 the clearance of older engines, that is so the new fuel saving thin oils can be used.