I had the same exact problem this past year. I couldn't shift into 4-HI other than very slow speeds. Then when I shifted back into 2 wheel drive, it would pause anywhere from 10 seconds to a minute, then a huge KLUNK. If I was on a trail, I could slow roll in reverse and shift into 2 wheel and it would shift without the klunk.
I know this won't help, but since I put in a SYE with the lift, it doesn't happen anymore, it shifts like new. Maybe something is slightly out of place in the transfer case. Couldn't tell you what was wrong.
2000 TJ, 4.0L, 5 speed
4.5" RE Extreme Duty Long-Arm
1" M.O.R.E. BL, 1" M.O.R.E. MML
Nth degree Mobility shock shifters
AA SYE/Tom Woods Shaft
33" Goodyear MTRs on 15x8 Cragar 352s
3.73 gears, D30/D35
2 PIAA 540 Driving Lights
4 IPF Lights
2 Stock Fog Lights
4 Rock Lights
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