New Clutch, slipping sometimes in high gears

Yes, new throw out bearing comes installed on clutch assembly. It’s not like a car where you install it with the clutch. It’s part of the unit. It also comes prelubed but also still need to grease it after install. Just saying, even if they didn’t grease it, there is no way for it to have failed already. It’s common practice to install Eaton clutch install kit as well which comes with new input shaft and bearing as well as forks. You had a new trans installed so it should t have needed that. If the cross shaftsbushings were bad, then you just replace those in the bell housing. They are cheap.
First pic is clutch assembly with throw out bearing on top. Second bearing is Eaton clutch install kit which you shouldn’t have needed. The only reason you would have needed new clutch forks if someone was double clutching that rig all it’s life and wore out the tabs

 

This is the reason I work on my own truck. I seen plenty of times from co workers where they took there trucks some where to get a simple clutch replacement and the truck comes back in worse condition. I guarantee you are more of a mechanic that’s whoever worked on your truck. You never know where these clowns screwed up and giving you troubles

 

So the knocking sound when the clutch is depressed is the fork making contact with the clutch housing. This happens when the clutch control, idle shaft, and bushings are not replaced (or properly replaced). I saw this a hand full of times when I was a “Noob that thought he was professional”
As for your no clutch engagement. I’m not really an expert, I’ve only read about hydraulic controlled clutches. But I would guess your no engagement is caused by something in the control system. Could be a pinched line, but that wouldn’t be as inconsistent. My best guess is you have moisture /condensation in the hydraulic guild that is freezing and working like a check valve. It may just need the fluid flushed with new and have the system bleed out.

If that doesn’t fix it then it could be either the master or slave cylinder hanging up.

Or one final thought, it maybe that since your clutch fork control shafts and bushings aren’t done right, it’s allowing either the fork to cam over, or the shafts are binding hard enough to hold the clutch released.

But again, I’m not an expert on your hydraulic control system.

 

First the clutch should never slip if it is new.

Don't care what others say, the clutch is a friction coupler it is design not to slip out of the box and properly adjusted. Adjustment after that takes place when clutch plates are worn and the clutch plate is adjusted to compensate for the wear. If it is worn and the clutch plate can't be adjusted, then the unit is replaced.

I've seen a lot worst with the clutch plates you posted. But I can tell you they never replaced the clutch or pressure plate, just threw in the old one, I had this done to me a few times when there was a seal problem and the clutch wasnjust washed with brake cleaner and replaced, which it failed less than 10k.

Second the trans they put into the truck is used and cheap, they did it to dump the truck.

Why would you need to replace the trans?

You drove the truck six months before you purchased it so you can answer that, did it grind or did it pop out of gear?

Go to the dealer and have the clutch properly adjusted.

 

Very easy to tell if the trans was replaced by a new or rebuilt one. It will be painted and new tags on it with serial for warranty purposes. That’s for starters. If you suspect it was a rattle can overhaul, just get the serial numbers off the reman and call the manufacture to verify. I’m just gonna give the op the benefit of the doubt to at least look under the truck when he picked it up to see if trans has nice new paint job. And if suspected trans wasn’t replaced, call manufacture with serial number. Pretty easy to tell if clutch is fairly new by looking in inspection cover as well