You are pushing against the rotation of the transmission when going into the upper gears. When you pull with it in the lower gears, then it is smooth and jumps into place. Or that's what i would think.
It would have a sm 465. Its a heavy cast unit with low (granny gear) and three other forward gears plus reverse.
Well, that vehicle would have had a TH350 trans. So, it would have had 3 forward gears, and then a 4 low in the T-case, so actually, you could split each gear in the trans, making 6, actual forward gears. And then, actually, 2 reverses.
Tranny is going out
The transmission is broken. Take it to a shop.
If this is an automatic transmission, more than likely the transmission is on it's way to the junkyard. Usually failing transmissions lose reverse first, then the higher forward gears - last will be the lowest forward gears.
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Burnt forward clutches/ The forward cluth pack is stuck/welded together.... You need a overhaul...!
Have your universal joint checked first, then your differential, then move on to anything else. Universal joint replacement is fairly common for all models of manual trans. Jeeps as they gain some miles.
If you have the manual transmission 5 forward and one reverse, add to that 4 wheel high, 4 wheel low, and 2 wheel low, and I guess it would all add up to 24. But 5 forward and one reverse with a 4 position transfer case is probably what you are looking for.
I had a similar problem and it was my coil pack
Perhaps you are not easing off on the accelerator when using the clutch. you would get this from a worn clutch .
a faulty torque converter, faulty fluid pump, broken input shaft, worn forward band/Worn clutches/Low fluid level