Have you changed diff fluids? My 01 was 'stiff' at best a few years ago. It would shift in/out with a struggle and few minutes. A couple diff fluid changes and repeated attempts especially including a mild turns yielded consistent in/out of 4wd. It's on demand now, i think po didn't ever use it.
Luck and enjoy that runner.
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2001 Limited 4WD - 346+K - SunfireRed\Thunder Cloud; - 265/75/16 Michelin A/T2s - Fat Pat's 1.5" BL - StopTech ANGLED rotors - In series 699 trans cooler, New Yota1 transmission, All new OEM suspension front to rear.