You may have to "back off" your jake adjustment screws, to get a accurate valve lash on your exhaust valves.

Personally, I back off all Jakes screws 1/2 -1 full turn, before I even start with any adjustments.
 
When you have your .030" feeler gauge under the exhaust rocker, just make sure that Jake slave piston "foot" has clearance/air gap, between it and the rocker(top part of the rocker), while setting each exhaust lash, then you know the jake adjustment(slave piston) is NOT interfering with your exhaust lash adjustment.