How to replace bearing in a 1991 chevy 1500 4x4 rear axel at driveshaft?

I'm guessing your you are referring to the drive shaft center support bearing. Remove u-joint 4 bolts at rear diff., then 2 bolts for center support. Slide driveshaft assembly out of trans. and lay on ground. On either side of the center support, make alignment marks on front and rear half of drive shafts with a crayon or tape (very important for re-assembly). Slide rear half off. Press out center support. Clean sleeve with emery cloth or 400 grit sand paper. Press on new center support, lube splines and reconnect drive shaft halves making sure alignment marks meet. Install assembly and torque bolts.

look in rear diff. worn gear is binding up. not going to last long. fix now before it blows the whole carrier and everything.also A worn U joint in driveshaft could cause this

For the rear diff., remove the driveshaft, brake drums, diff. cover, remove pinion flange nut, move diff carrier to access side gear retainer bolt and remove bolt, slide side gear pin out and push axles in to remove axle retainers and remove axels. Mark carrier bearing retainers, spin bearing retainers to loosen carrier for removal. Remove carrier, remove pinion out of diff case, then r&r bearings. Any shims should be replaced in their original location for depth and pinion to ring contact.

driveshafts as in tailshafts? or axels from diff? if its just the tail shaft, it just has 4 12mm nuts and bolts, one spanner will get it out make sure you dont lose the spring washers and try support it when removing to prevent damage to the centre bearing.

The rear axle seals are leaking too,it's been my experience with Dodge 2500's,all 3 seals leaking is usually a indication that there are bearings going south!

if there is some one in your area that balances driveshafts they can change just the bearing for you

Check the U-joints in the driveshaft.

the outer bearings can be driven in using a suitable Very Large socket. Removing the old ones either requires a puller or a cutting torch. I use either depending on the state of the bearings.
when driving new ones in, make sure

1. your socket wont jam in with the bearing
2. you only hit against the outer bearing shell
3. you keep it very straight
4. hit it til you hear a resounding solid clunk as the bearing reaches full insertion.
5. you fit a new oil seal
6. use a block of wood across the oil seal face to protect it as you knock it in - keep it straight!

To answer the other question, yes you do have to remove the driveshaft to replace the oil seal. the Diff ack-plate has to be removed, the locking horseshoes from the ends of the driveshaft, & the wheels. It takes about 1 hour to remove them & clean the backplate. about another to reassemble.
I charge about $140 plus parts

JACK UP VEHICLE, BLOCCK OTHER WHEELS. REMOVE DIFF. COVER & PLACE VEHICLE IN N. USING A BOX. END 8MM WRENCH; ROTATE DRIVESHAFT TO YOU LOCATE CARRIER RETAINING BOLT ON RH SIDE OF CARRIER. THIS BOLT HOLDS TO RETAING PIN IN CARRIER, APROX. 1/1/4" DIA. REMOVE PIN. PUSH BOTH AXLES INWARD. LOOK INTO CENTER OF CARRIER WHERE AXLES MERGE. EACH AXLE WILL HAVE A RETAING CIRCLIP. REMOVE EACH CLIP & PULL AXLE OUT ABOUT 1 FOOT. REMOVE REAR DRIVESHAFT & SHAFT YOKE @ FORWARD PART OF DIFF. A SPECIAL PULLER IS NEEDED. NOW YOU CAN REMOVE THE 4 BOLTS HOLDING CARRIER TO DIFF HOUSING, PREY OUT CARRIER ASSEMBLY, USE CAUTION- ITS HEAVEY!!

cut it off and dont worry about it.put on a new boot clean greese.you will not notice anything with that off the axel.i have done it many times