Clutch issues, need help!

[BKs50trimGST]

this has happened numerous times in the past two months. Scenario: I'll be driving on the highway for about 20min. at a constant 55-75mph, then when i wanna downshift or put it into a different gear it won't let me do anything unless i pump the clutch, the clutch itself feels really loose/soft like there is no pressure, when i swapped my 7bolt for the 6bolt i have now i also replaced the clutch master cylinder, so i have a brand new one in there, could it be faulty install? tranny maybe going? please help me, i need to fix this problem. it's been getting alot worse lately to.