I just did mine and had the same problem. What I did was compress the spring enough to loosen it, remove the nut holding the shock on, then loosen the spring compressors. Eventually the spring just pushed it off. Don't worry, it won't fly off either.
Black 2000 Trans Am, PRC 5.3L Stage 2.5 Heads, LS6 Intake, TR231-235/114+2 LSL Cam, McLeod Street Twin, LTs, ORY, Hooker Catback, TNT 150, Ford 9 TrueTrac w/ 411s, Strano springs, Koni, LCAs, Spohn TA.