If it is a 4 cylinder then the answer is that this is a woefully underpowered engine, which has a measly 123 H.P. & 139 Lb/Ft of torque. If you encounter any sort of incline it will loose power very quickly. If on the other hand it is a 4.0 in-line 6, then you may have a partially clogged exhaust system. Take a close look for a bent pipe or have the catalytic converter checked to make sure it is not clogged. It may also be starving for fuel or air. Replace the air filter and fuel filter and see if that helps. It may also need a tune up.
The LS has a five speed transmission. Therefore it shifts from first to second, second to third, third to fourth and fourth to fifth. Four shifts.
Stick shift.
Engage the clutch. Shift to neutral. In neutral move the smaller shift lever. On an 87 wrangler the lever is closest to driver. The shift pattern is 2H at the top, 4H middle and 4L is all the way down.
Your synchro is going bad.
You may have to have your clutch adjusted,
If a 2000 Jeep Wrangler suddenly loses power in 5th gear, it might be a problem with the speed sensor on the transmission. This sensor regulates when the Jeep will shift or should shift.
It wants you to shift...I don't pay attention to it because it will tell you to shift when rpms are too low or high so it will drive you nuts if you try to shift with it.
You pull the transfer case shifter from 2wd to 4wd.
If it will shift when the engine is off, but not while it is running your clutch is not working
In vehicles with a five-speed automatic transmission, keeping the gearshift in "D4" will cancel the fifth (or "overdrive") gear keeping the vehicle in fourth gear; this setting is recommended when towing trailers or boats to keep the transmission from overheating.
Reverse is top far left. Lo is directly underneath. first is top middle, second is bottom middle, third is top right, fourth is bottom right. in high range, fifth is where first is, sixth is where second is, seventh is where third is, eight is Where fourth is.
your shift lever bushings are bad, easy fix.