1993 Isuzu Trooper stuck in 1st/2nd gear

1993 Isuzu Trooper 3.6L V6 89000 miles. My vehicle seems to be stuck in 1st/2nd gear. The shifter lever will not go into 1st or 2nd, but when the lever is floating in Nuetral it will go forward when you let up on the clutch. The lever doesn't seem to go into 5th or reverse either. It will go into 3rd & 4th but when you let up on the clutch it only spins. It also doesn't seem to engage in neutral either because the vehicle will die when you let up on the clutch in any position. It had to be towed backwards because the rear wheels were engaged. The vehicle was/has been running perfect. I went to make a 3 point turn on a down hill incline when this happened.I went forward, back, forward and when I went to reverse again is when it happened. I have already disassmebled the shifter lever and removed it, there is still another metal cover bolted to the transfer case (I think), before I go any further I would like some advice. Any help would be appreciated. Thank you Tambra