Asap! Why won't my truck shift out of 2nd!??

[Heavy87Chevy]

I was driving for about an hour at 90 kmh and all of a sudden after going up a hill, my truck wouldn't shift back up. I checked the tranny fluid which was low & stopped, put in 2L of fluid which made no difference, but it says the level is good on the dipstick. Wtf is happening? I've put maybe 5k km on the rebuilt 700r4. I'm stuck an hour from home now unsure if it's safe to drive home at 50km/h. It won't shift out 2nd at all & the 1-2 shift is hard. I had this problem before the trans got rebuilt
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