There are three options: "FE1", "FE3(Sonic RS)" and "FE4". I have installed the GM Performance Suspension which replaces my 1LT - FE1 suspension. The GM Performance suspension is above and beyond the FE3. It contains new rear shocks, front struts and 20mm lowering springs. The issue in question, does the new GM Performance suspension (GMP) now carry the RPO designation of FE4? Or should those installing the GMP suspension use the FE3 specs? The FE3 to GMP upgrade includes 10mm drop via springs with upgraded rear shocks.
Clear as mud?
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Clear as mud?
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