do I need to reset my computer after installing a K&N intake system on my 99 Chevy Blazer V-6?

The computer will auto adjust to the increased air via the MAF sensor (hope its still in the intake- and the temp sensor too). excess oiling of the K&N can cause the mileage to drop if the MAF gets oil on it - if you have this occur clean the sensor (no carb cleaner - only MAF , electronic or brake as no residue)

Yes, I would reset it so it will relearn the fuel curves faster.

It will eventually do it if you don't reset, but resetting make the process much faster.

after any engine mod its always a good idea to reset it. the computer will relearn the new paramiters much faster. welcome to af by the way.