w valve train off leakdown is good which tells you the long block (incl the valves in Q) are sealing. Setting #1/#5 cyls on TDC compression one at a time of course can you see what is holding the valves open? how much preload/can you move the p rod(s) down further by hand. From your descrip it almost sounds like the cup/plunger etc in those 2 lifters are hanging up even tho on dissassembly they looked OK