it sounds more like a a clutch problem or through out brg problem

what is happening it the clutch disk it still holding to flywheel or pressure the common causes are either bent drive straps on pressure plate causing pressure plate not to lift evenly or hyd clutch not fully disengaging clutch. as you has discribed it gets worse when warm I figure it will be related to the hyd throw out brg system does the clutch pedal feel normal or very soft. If very soft then if sounds like there is still air in system and it needs bled. if pedal appears normal it can be related to actual throw out brg travel not being enough and this can be cause by several different things. Flywheel machined to much, wear in throw out brg, incorrect throw out brg, inproperly adjusted pressure plate. Biggest thing is at a stop push pedal to floor allow a 5 sec count and try to put into gear 1st or reverse if it will not go or grinds then the clutch disk is still spining to fast and problem is clutch related

hope this helps