[lurkingknight]

manufacturing tolerances are off on the new gearbox shell. It could be that the whole switch assembly sits higher than in the original. Try rolling the trigger trolley spring the other way so that the loop that hooks onto the trolley connects to the rest of the spring on the bottom. Sometimes that makes all the difference as the spring tends to want to lift the ass end of the trolley up off the trigger. Also maybe pry the contacts open a tiny bit so there's less resistance for the trolley. You want the trolley to kiss the contacts instead of being pinched. Once you get the trigger responding, re-evaluate the cutoff lever. It might just be time to change it and the slight out of tolerance is making it more apparent, but until you get the trigger behaving as it should, don't try to diagnose it.