LT77 crunching after rebuild

alright. Ive jusu had my lt77 box rebuilt after spinning the mainshaft, due to the splines wearing through. Anyway, got my box rebuilt at a local gearbox specialist. Dropped it back in with a new clutch, fork, master cylinder and slave cylinder, as they wer both original units and had leaks on them. Now the box is in, and filled with difflock evo1 oil, down shifting from 4th to 3rd just crunches like mad, if i am doing over 25 mph. If i double clutch or change really slowly it just about goes in. The same happens from 3rd to 2nd when goin over 15 mph. Surly this shouldnt happen after a full rebuild? Going up through the gears is fine. I phoned the gearbox place i got it done at, and they say the clutch is at fault? But all clutch components are new, and is fully bled up. Any ideas? Should i take my truck back to the gearbox place and get them to drive it? any advice would be appreciated

doesnt sound like clutch ,clutch not clearing would lead to gears not going in, in a jamming feel not grating noise ,sounds more like poor baulk rings,or wrong oil did you use dexron 2 or 3 atf ? , baulk rings tapered and should grip gear cone and act like a brake so gears are synchronised speed wise ,grating comes from them not doing so

I put difflock evo 1 oil in it. I thought i would splash out on some good oil for it. Yeah, i thought it would be down to the bulk rings / synchros, ive rebuilt over boxes in the past, so i know how they work. Would it be down to poor quality synchros or not properly fitted / spaced?

h suffix 1st and 2nd can be tricky as are a compound set up and need to be kept straight while fitting rear bearing other wise they can get distorted ,but others are just fit no setting up or adjustment, there are alot of poor rings for sale