If you're just replacing u-joints, you don't need to remove any part of the transmission. The tail shaft is the output shaft of the transmission. I think you're referring to the driveshaft, since that's where the I-joints are.
First, raise the rear of the truck so your transmission oil won't drain out once the driveshaft is removed. Unbolt the flange yoke from the differential pinion flange. If it's a long bed, remove the two bolts holding the center support bearing. Then just slide the shaft rearward. The front is a slip yoke that mates with the tail shaft.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com