My 98 sierra was leaking water from intake,carried to shop replaced gaskets,and now engine misses not when cold or at fast rpm but slow. replaced wires,plugs, cap, and rotor had to put original cap and rotor back.still misses

might have a weak fuel injector. i've seen a few injectors get messed up after doing the intake. if you haver access to a scan tool and fuel pressure gage you can do the injector drop test, or get a shop to do it if you don't have the tools.

You may want to post in this forum too.... http://www.automotiveforums.com/vbulletin/showthread.php?p=2613117#post2613117