5 speed tranny

This sounds like you may have a problem with the shift linkage and when you jack up the car it is taking the pressure off of linkage and frees it up, I am not for sure but some have adjustments that can be made to fix the problem. If that's not the problem then you may have a problem with the trans itself. If you can get to the trans you could unhook the linkage and try shifting the trans with the conectors coming from the trans.

The trans has to come out & come apart
& be gone thru to replace worn gear syncros
& any other parts

To be that bad in all gears, it hasn't been treated
very well

Never use a tool myself other than a big hammer. Those forks don't work for me, though we have them. Hit the joint on the side and it will pop out. If not, you can always put the nut back on even with the ball stud and hit it from the bottom. The book also calls for a special tool to get the axle out of the hub. Have never used this either. If it doesn't slide out, I just hit it--I have a new one anyway (take it loose from the tranny before hitting it). Tools you will need are the big socket for the axle nut (around 22mm or so) and regular metric socket set, preferably 1/2 in drive. Also take the speed sensor and brake lines off the support bracket to free up the hub a little more. Note that you may need to also separate the tie rod end if you cannot otherwise swing the hub out far enough to get the shaft out. The book says to take off the stabilizer and shock and also separate the upper ball joint. I don't know if that's necessary or not, as I have not done one on this particular truck. You are doing the whole shaft, right? We don't do individual CVs anymore, as the labor is ridiculous compared to the cost difference to a whole half shaft. Take the axle nut off, unbolt the shaft from the tranny, and swing the hub out. Pull the axle out of the hub first, then the tranny. Reverse procedure to install. I will paste the book solution from autozone.com below. Lemme know if you have more questions.

1. Before servicing the vehicle, refer to the Precautions section.
2. Remove or disconnect the following:
   
   Front wheel and tire assembly Skid plate, as required. If equipped Drive axle hub nut and washer Brake line and wheel speed sensor support bracket from the upper control arm to allow extra travel of the control arm. Left outer tie rod attaching nut and cotter pin. Separate the tie rod from the steering knuckle
   
3. Position the tie rod aside and push steering linkage to the opposite side of the vehicle.
   
   Lower shock attaching nut and bolt; position the shock aside Left stabilizer bar bracket and bushing at the frame Stabilizer bar bolt, spacer and bushings at the lower control arm
   
4. Taking pressure off the upper control arm by placing a support below the lower control arm between the spring seat and the ball joint.
   NOTE Cover the shock mounting bracket and lower ball joint stud with a towel to prevent the axle boot from tearing during removal and installation.
   
   
   Upper ball joint cotter pin and loosen (do not remove) the upper ball joint attaching nut. Separate the ball joint stud from the steering knuckle. Remove the attaching nut.
   
5. Separate the axle shaft from the hub and rotor using tool J-28733 or equivalent.
   
   Axle shaft inner flange bolts and shaft
   

To install:

1. Lubricate the axle and hub splines with an approved high temperature wheel bearing grease.
2. Install or connect the following:
   
   Axle shaft in the hub Inboard CV-joint-to-flange bolts. Torque the bolts to 60 ft. lbs. (80 Nm). Upper ball joint to steering knuckle. Torque the stud nut to 61 ft. lbs. (83 Nm). New cotter pin through the upper ball joint stud and nut, lubricate the ball joint as required. Left stabilizer bar bracket and bushing at the frame Stabilizer bar bolt, spacer and bushings at the lower control arm Lower shock in the mount bracket and the attaching nut and bolt Left tie rod end at the steering knuckle. Torque the nut to 35 ft. lbs. (47 Nm). New cotter pin through the tie rod stud and nut Brake line bracket to the control arm, ensuring the line and/or hose is not twisted or kinked Skid plate, as required Axle hub washer and nut. Insert a drift through the rotor vanes to keep the axle from turning. Toque the hub nut to 180 ft. lbs. (245 Nm) Wheel and tire assembly
   

ive heard people say that on a auto transmission on a BMW that if it wont go into reverse there might be something wrong with the transmission... just a thought, i might be wrong

Most likely an internal gearbox problem, but I would first check the shift linkage at the gearbox end, see if you can disconnect it and change out of reverse from there.

Internal damage to tranny. Is this original top loader or after market tranny? Really doen't matter - take it to a transmission repair shop unless you can pull it and take it apart.

Can;t be sure on this one except to tell you that you may have a bent or broken shift fork in the tranny. The only way to find out is to remove the shifter from the top of the tranny and see if you can see the fork and move it in and out of gear. If not the next step is to remove the tranny and take it apart. With the information you gave that is about all I can help you with unless there is more info you can give to me.

It could be that your syncro for the reverse gear is gone. Which would have to be brought to a tranny shop not a do it your self type of job.

Transmission are kinda tricky. Yes you'll have to take the t-case off. Transmissions won't just fall apart when you break them open. But first things first. What's it doing. And if you don't really know anything about transmissions, I would give it to a shop to rebuild. Won't cost very much.

Are you sure that it is gone? make sure the all the bushing on the transmission are good it maybe that it is not able to go all the way in gear. If you do need to take it out get a good manual "Bentley" are the best it will show you the inside of the transmission too. Haynes are also good but not for working on the transmission it self