Need 4-speed Help

Originally pulled the side plate off to look inside for anything obvious such as missing/ground teeth on gears, excess metal fragments inside casing but other that that, wasn't sure what else to inspect for. The ratcheting check balls fell out and were almost left in the case, but luckily noticed before I closed it up..

This is my first 4-speed and the clutch assembly seemed fairly straight forward, but is there something that I could have overlooked for the clutch to be slipping?

Also, was planning on ordering a rebuild kit from Brewers or Passon, just not sure if there is something else that will be obvious during the rebuild that I should be looking for that would cause the substantial slippage or squealing noise? I have the Mar 04 Mopar Muscle tranny rebuild artical as a reference, but not sure if that along with some common sense and some basic orgaization skills will be enough to trouble shoot or rebuild..

Thanks for all your help!