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There is no real way of knowing if your previous oil changes have been done properly, getting an oil sample analysis done might give you some clue.
The sluggish feeling after the filter was changed is most likely just in your head, no offence intended it's just very unlikely changing the filter on its own would have that much affect. Which warning light flashed on?
This photo shows where you can block the EGR. It is under the I/C on the drivers side (RHD vehicles).