I don't think its anything to do with half time team talks or tactics.I would say the following factors are more pertinent;
1.Argyle have had nothing on the bench this season to change games,a luxury which opposition managers have enjoyed.
2.An awful lot of crucial goals have been scored [Gillingham,Swindon,Morecambe,Cheltenham spring to mind readily] VERY late in games.To me,this suggests that there must be a fundamental problem in the squad with the physical side of the game-if it was a tactical problem brought about by something lacking in the half time team talk,why did it take opposition managers so long to suss this out? I don't mean just the ability to run for ninety minutes,thats not a problem.The strength and stamina issue must be relevant-Argyle have had a lot of young,lightweight players on the pitch this season,mostly through necessity rather than choice.And i'm not sure if the pre-season preparation was what it should be with all the off field shenanigans-anyone who has played football to a decent standard will tell you that if pre season is not up to scratch for any reason,then it can be very difficult to catch up,no matter how old or young you are.
3.The inability to bury teams when they are down.This may well be all interlinked to the issues in paragraph 2 but it has been a trait in Argyle teams of recent vintage to sit back and hold on to leads,rather than try and put the boot in on the opposition.Don't really know why,it seems to have been the same no matter who is manager.
Hopefully the arrival of some players with a bit of physical strength will put matters right,although it was disappointing even on saturday that a late goal was conceded-its a trend which must be discontinued if Argyle are to make headway and secure their status this season.