Ok my truck sat up for about 2 years with out hardly any run time. One year without touching it. Decided to try to get it back on the road after 3 years. The motor developed a ticking sound on the drivers side. When you would try to accelerate it’d start dropping a cylinder and backfiring thru the exhaust. So kept running it and it got better. Not so much backfiring anymore but the tapping is still there. Changed the oil several times and the tapping is still there but the backfiring hardly happens anymore. Truck runs perfect besides the tapping. The other day I took it out of overdrive and let her stretch her legs. At 5200 rpms I felt it starting to drop a cylinder and the backfire was pretty bad. Let out of it and let it shift to overdrive and motor is running fine. No missing or backfiring. I’m leaning towards a lash adjuster is gone and won’t hold its prime. I doubt if it’s a bent valve or guide since it’s not constantly missing or backfiring. I’ve put all new plugs, coil packs OEM, checked all I could think of. Any input?