Sounds like the coils to me also... FWIW it was very easy to change the coils on my '97. Look at the coils and follow the wires. If you have misfires on multiple cylinders and they are on the same coil then thats probably it.


Also, from what I've seen, clogged or inoperable EGR won't cause misfire or bad engine stumbling. I've run with the EGR vacuum line disconnected for months and never had a problem. When I fixed the problem the engine light went out but the truck ran just as good.

As far as detecting clogged CATs... from what I've seen... if the vehicle has clogged CATs it slowly start to lose power over a period of weeks or months and then all of a sudden the engine will start to misfire and run rough. If you drive it around like that until it gets good and warmed up, look under the vehicle. You may see the CATs glowing red hot like I did.