You're not going to like where they are at. The transmission has 2 pans. One on the bottom, and one on the side of the transmission(driver side). You need to remove the side pan to access all of the solenoids. This involves either removing the trans completely, or just lowering that one side of the whole engine/trans assembly out just enough to remove the pan. Either way, this is a in depth task that requires tools, jacks, jack stands etc etc.
Yes, there are 2 shift solenoids. I don't recall if they are both the same. But 3rd one you need to replace is the TCC. Torque Converter solenoid.
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2000 Chevrolet Blazer LT 4X4 4.3L
2002 Chevrolet *-10 LS Ext Cab 4X4 5.7 V8