I went through all this with my 2wd, only running greens & t34
The new std clutches just aren't upto it, I tried brand new motorcraft and luk covers with both std and an ap 6 paddle centre and it still didn't work. Always slipped in the higher gears on the motorway.
After taking the box out for the 4th time enough was enough and I put an ap heavy cover in it. Was fine after this.