2011 Tahoe 5.3, #4 cyl lifter

I was drawn to this group through the mutual problem of DOD/AFM. My engine developed the lifter tick in an instant. It has not progressively gotten worse over time. My Tahoe has 260k miles and ran great until the P0304 #4 cyl misfire code. I had to take a crash course of sorts on the internet to understand the operation of the AFM/DOD system. I have a son that is a decent mechanic, and I tinker as well. I bought the Tahoe with high mileage ( I drive very little since retiring) and the intention if I started experiencing costly issues I would just find a salvage yard 100k mile replacement engine. Trying the lifter unsticking may buy me some time, but no guarantee it won't return. I think a proved running replacement engine might be the better gamble given the 260K. Murphy's Law always prevails with me, my luck would be new lifters, trays, VLOM, gaskets etc and then have another issue immediately after buttoning up. My oil pressure has dropped also, rarely hits 40, hovers around 25 or so. VLOM bolts loose. Makes me wonder if the screen on the VLOM is clogged, or the oil pick up tube o-ring is bad, sludge in the oil pan? I'm an old man, if I can get 50k miles from an engine now it would take quite a few years for me to drive them. I want the higher gas mileage of the DOD, was getting in the high 19's last long trip. I am retired and am not performance minded any longer. I also just want the best bang for the buck without alot of time wasting trial and error. In my area I can pick up a good engine for $12-1500. There has to be a point when you decide to just replace the engine. I have seen many that have more miles than me still going strong. There is nothing to say a replacement engine wouldn't develop the same issue eventually since it is a known fault. I haven't decided yet what approach to take. Maybe your responses will help me decide. Hats off to all the time and effort you have spent on these issues.