The last time I ran a hydraulic roller I went though the samething The cure was 1 to 1 1/2 turns of preload witch is .042 to .060 preload with a 3/8 24 thread adjuster. Chrysler had the same problem with there first roller motors in the late 80s. They recalled the 318 and put longer pushrods in them. The only other thing I can think of is if your lifter and pushrod have the holes for oiling through the pushrod you could be bleeding off to much oil pressure to the top end.