Smoking Clutch, Clunking while shifting

I've owned my truck for about 6 months now, and have put on about 5k miles. The previous owner claimed to have replaced the clutch himself at around 125k miles and it now has 140k miles. It's a 1999 4 cylinder 4wd, stock 4.10 gearing with 32" tires.

I first encountered this problem last winter screwing around in parking lots in 4wd nearly bumping my rpms off the limiter, the clutch started to smell real bad. It went away after a little while and I disregarded it until I went to the dunes last week and, getting out of a deep, sandy section with the wheels spinning like crazy (I'm supposing, since I was WOT at 5k rpms 4hi, 1st gear, and moving really slowly). When I got over the crest there was a smoke coming from under my hood and the godawful burning clutch smell.

The next day I drove 400 miles to Seattle, notorious for horrible traffic and steep inclines. After being in traffic for half an hour, I pulled into a parking garage to the wonderful burnt clutch smell.

Ever since I bought the truck, it has clunked while shifting IF you give the throttle gas to get the rpms to match the road speed. But IF you just engage the clutch without giving any gas, it syncs up smoothly.

I did a few clutch tests and I don't think it's slipping, but it does seem the friction zone is much smaller than before.

What's going on here?

 

Dunno if thats right or not, but you may want to check into it.

 

I would recommend changing the clutch, and maybe replacing the fly wheel. sound like a burnt clutch. Iv only had mine on for about a year now, and im not going to use this clutch again.