Another question- can these blazers be de-tuned in order to comply with emissions or anything like that? My '99 is still sluggish uphill, feels like it's either surging or missing & feels as though there are "dead parts" in the throttle

I read your post and feel your frustration on having a problem and not knowing what part to replace. Here is a helpful site which is specific to GM Vortec 4.3 L V6 and tells you how to test parts rather than replace $$ them. It is Troubleshootmyvehicle.com and you then go to GM and then to 4.3L, 5.0L, and 5.7L for the Vortec engines. There you will see a index of articles for the 4.3 V6 Vortec engine. One article you may like is how to test the ICM on 95-05 4.3 engines. It also covers head light switch , the TPS test, the ECT sensor, how to test the blower resistor, the misfire by the Spider, MAP sensor test, and so on. If you read this forum, you have heard many of these complaints.

Part 1 -GM 4.3L 5.0L, 5.7L Index of Articles