What year is your Blazer? At what temp does the problem happen or get worse? Are you getting a service engine soon light? Idle quality is controlled by the idle air control valve in the throttle body. If it is bad or dirty you may have slower response from the valve. Try removing it and cleaning it and the passage for the pintle in the throttle body. Of course there are other things that can cause your problem, but there's a starting place. Your post sounds like you had tuned it up somewhat recently so we can skip that. Maybe check your spark when you let go of the throttle. Also your tps is important with metering fuel, if it's going bad you may have a problem there as well.
BTW the 2.8 is a v-6