88 Bronco 2 Help I have drive train prob

Well hopefullysomeone else has had the misfortune of having this problem..1 year ago I was driving my 88 B2 5sp 6cyl while in 4th gear i noticed the engine rev up like I had put it in neutral. I let off the gas and pushed it back in and it seemed to engage normally. I assumed the clutch was wet and it was slipping a little bit. Made it home no problem. The next day i drove as normal and the problem did not reoccur. The next day I was driving and in 4th gear it happened again. I let out and pushed the gas back in but it did not engage. I downshifted to 3rd and it caught. So i contined home and as I continued the 4 miles home it would not catch in 3rd any more... down shifted to 2nd it held for awhile and finally did not hold at all. coasted into the driveway puzzled that I was in first gear and the clutch was not pushed in and it was sitting still. I checked on the rangerstation.com web site and it was suggested it was the slave cylinder. So I saved up some money and went and got a slave cylinder. Dropped the tranny and t-case and put it in. I bled the slave cylinder and it seemed to work. I backed out the drive took off down the road and it seemed to be fixed... as I was reaching over to pat myself on the back in 4th gear about 45sec to a minute later it did it again. I continued down to the gas station and put gas in. i left it running and after putting in a few gallons got in put it in 1st gear and nothing happened. I tow-bar'ed it to a tranny shop and they said I needed a new clutch and for $500.00 they would put one in. Well being 20 years old and not having an extra 500 bucks laying around I towed it home and started saving money to buy a clutch kit. So I saved up the 100 bucks bought the kit dropped the tranny and t-case and put in the clutch, pressure plate, new slave cylinder, and had the fly wheel resurfaced. I put everything back bled the slave and hopped in and it took off...drove around the block a few times and on the 3rd time it slipped again WTF! So now, here I sit with a 4WD B2 lawn ornament. I don't have the cash to take it in and have it done so I need some help trying to figure out what it could be. Any ideas i would appreciate it.So it feels like a clutch not engaging at all. thanks in advance for the help