When I first start my yukon it has 45 pounds of pressure but when I drive it the oil pressure goes to 10

With fuel injection if the pressure goes to low the fuel pump will stop and the lifters will get noisy.If you are seeing 10 lbs hot at idle I wouldn't worry to much.
If you have a high mileage vehicle and live in a warm climate,go for 20w50 oil at your next oil change,some use straight 40w oil to help oil pressure on worn engines.

Oil pressure drop after reaching operating temp is normally caused by worn main bearings (depending on mileage).Worn bearings will allow pressure drop at idle and increase when accelerated above idle.

take all wheels off the ground use jack stand,start engine up and put car in drive and let it run for about 5 mins, with wheel off the ground it should shift gears better, if it do you to change your transmission filter and oil, VERY IMPORTANT TO CHANGE OIL WHILE IT IS HOT! check oil to make sure no metal is in oil or heavy shavings, if shavings or metal is present you need new tranny,measure the amount of oil you take out put same amount back in, i really dont think you got a speed sensor problem you might have too much milage on your yukon, hay mon sure you service your yukon on time or else ford will excort you home, good luck mon and big up u self

If this truck has the 4.3L vortec motor it will not start with 40-45 PSI fuel Pressure.Thius engine requires approx. 56 PSI fuel pressure or it will not start. The fuel pump more than likely needs to be replaced this is a common problem with the 4.3L vortec engine.Change the fuel pump and your problems will be solved.

dont be messing with different oils, it needs 15W40. period. these trucks have enough problmes without putting in the incorrect oil. First get the right oil in it, then have a diesel shop check it out.

I have a 99 blazer and ever since I have owned it, it reads lower in pressure when idling, but will go up too 40 while driving. This is normal for the vehicle. If the pressure gets real low, and stays low, it means its time for an oil change.

As long as the pressure goes up when you give it gas, it is fine.

Mate .2 things.The oil pressure sending unit is playing up or its not.The other is how long since an oil /filter change.If you know the oil is ok ,get the sender unit fixed.Oil is a lot cheaper than metal if things are not right.If it happens all of a sudden,the sender unit may be at fault.Hope this helps

2 things come to mide off the bat loose or corroded ground or cluster going bad

Well first the GM oil pressure sending units are notorious for false readings, so what you must do is remove the oil pressure sending unit and plug in a test mechanical gage to verify the engine has acceptable oil pressure, after you are certain the pressure is ok replace the sending unit, it requires a special socket to remove it, the socket is about $5.00 USD. There is a deep socket and a shallow, so check the sending unit for the correct socket fit.

i would check the the oil pressure sensor is not foul up this can happen sometimes, as there is vain in the sensor. this reads the pressure. and tell the ecu. and your display.