With the side cover off it should be pretty simple to check the lobe lift right at the lifter with a magnetic base dial indicator. If that comes out right, look for a problem with wear on the underside of the rocker arm where it contacts the valve stem. Uneven wear there can make it difficult to get a good lash adjustment.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!