AFM/DOD Q&A

Hello. I have a 2012 Tahoe with 150k miles. I had a collapsed lifter once where it was making the knocking sound. It took a few minutes and it released on it's own and ran fine again. I purchased the oil blocker plug and lifter release tool. I installed the plug and clipped all the vlom gaskets per the instructions. I sent off the PCM and had the AFM turned off. The vehicle ran great for a good while until last weekend. Now I have a misfire on cyl 6. I have done all the normal troubleshooting steps with everything working fine. The last part was to check valve train operation. Pull valve cover, use test relay and crank. Every time I crank the engine, the number 6 intake rocker works normally for 3-6 cycles, then stops moving completely, almost as if it is building oil pressure enough to activate the afm function of the lifter. Wait a bit and crank again, same thing, 3-6 cycles of normal operation, then stops completely. Could there be something that is causing the lifter to actuate without oil going down the oil tower. I should also note that the top end is very clean, almost looks new. I do plan on doing the full delete on this soon as I would like this vehicle to last a good long time. Any input you can provide would be greatly appreciated.