All gears act like neutral

I'm getting on the interstate in 2nd gear and I get on it just a little bit and then it starts to rev up so I let off and put it a 3rd and I started driving and it was fine, I was out with friends and didn't mess around the rest of the night and then picked up someone else told him it happened put it in 2nd did a couple 20-40 pulls to show him what I did and on the 3rd pull, all gears went into neutral including reverse tranny fluid is very light redish brown but no leaks anywhere. I can't tell if it's low or not what would be the problem? It also does not go into gear. It has around 4-5k miles on it rebuilt with hd2 trango kit shift kit