GMC C1500 TROUBLE CODE

I Have A 2003 Gmc Sierra 1500 2wd 4.8 And Im Having Trouble With Shifting. Its An Automatic 4speed. I Can Not Get It To Shift Into 3rd Gear...

I Don't Think My Truck Is Getting Enough Fuel Or Air Flow I've Been Told It Could Be Sensors But I Don't Really Know I Have Fault Codes But...