I just replaced the egr valve on my 98 s10 4.3. Now
when you rev the engine up it almost dies when it
returns to idle position. Then seems to idle fine.
The EGR tube may be clogged with carbon and the EGR valve may have been o.k. Only way to know is with a vacuum gauge. Other thoughts are you have a vacuum leak somewhere, Would inspect hoses for that. Good Luck!