Any chance both compression gauges are inaccurate? Unless I need to know the actual PSI of the cyliners (which then I'd use a known accurate gauge), I use compression gauges pretty much just to get numbers for comparing all the cylinders to see if any have a considerably different reading, regardless of the actual number. A failed injector could cause a misfire, it's not just an ignition-related issue. Unless your '99 has the injectors replaced/upgraded to the newer injector setup, it'll have poppet nozzles with a "batch fire" injector pod. The fault could be within this module.