What would you check next? Missfire on my 98

[leegreen]

I'll throw this out there. Can you actually feel/hear misfire?

Force the computer to relearn the crank position sensor correction factor.
If it is not accurate it can misidentify the cylinder or even the misfire condition. It has to know accurately when the power stroke from each piston is due to detect misfire. if you changed anything in the rotating assembly, sensor or computer itself the correction may be off.

Crankshaft Variation Relearn is a feature of some GM scan tools. I think the redneck way is to disconnect battery for a while, then drive around being sure to do some long decelerations from speed without brakes.

But I haven't done this myself, I know just enough to be dangerous, YMMV etc