Oil Pressure problems

[sanman4bama]

Hello everyone, I hope all is well. I'm new to the site and have an issue I would love to get some feed back on. I have an 06 GMC Sierra Z71. 5.3L with approximately 163,000 miles on it. A year or so ago I had my oil changed and within a week I had what sounded like a dry lifter ticking. No additives seemed to help. I took some advice from an old school mechanic and replaced a quart of oil with transmission fluid. After 800 miles or so the ticking stopped. I then changed the oil again and refilled with all oil. I've always ran 5w30 oil. I had my oil changed two weeks ago (change it every 7500 miles). While driving the interstate Saturday night my oil pressure gauge began to fluctuate extremely. 0 to 40 then back to 0, and the check engine light was flashing on and off. I pulled over and let it idle. Briefly the top of the engine seemed to be running "louder" than normal, and I heard a lifter ticking again. Then it stopped. For the next 20 miles or so everything was back to normal. Then it started to repeat the before mentioned activity. This morning when I started my truck there is 0 oil pressure and a buzzer was going off because of not having oil pressure. I pushed the accelerator to see if the pressure would increase and it did not. The motor was running "louder" again. It seems as though its not getting enough oil to the top of the motor. I checked the oil. It's full and clean. Needless to say I didn't drive it to work. I borrowed a ride for the time being. Any ideas as to what could be causing this problem? I'm almost certain it wouldn't be the oil sending unit. Could it be a collapsed oil filter? Maybe a pick up screen in the oil pan? Or could it be the oil pump going out? Any and all help would be greatly appreciated. Thanks in advance!