If the clutch won't totally disengage.....maybe the disk is in there backwards? On a V8 that can happen and it will act just like you describe...ask me how I know

70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"