Lot of wrong info here…. Band 13 is their 700Mhz spectrum the one they have had deployed almost everywhere for a while now. Repeaters you are technically not supposed to set one up without a licensed rebroadcast agreement from the provider as you can and likely are causing interference if you don’t have it configured properly.

Now can you connect to a tower that is 75 miles away is highly unlikely unless they have the tower configured to allow for that… I forget the specific feature but essentially they have to double the timing advance values as the standard maximum is about 36km. I can’t seem to find what it is I’m thinking of google keeps coming up extended cyclic prefix but I don’t think that was it.

TLDR: Your likely pointing your unlicensed repeater at something other than what you think you are.