I think the first place to look is the alignment of your dish.

75% is actually only a fair signal. I suspect if you had any kind of cloud cover or rain, the signal would break up. At my previous home, I installed the dish myself and got a 97% lock, and it held that for three years without any re-alignment.

At my present home, I had an installer do it (high on the roof). I get about 89%, and I wish it were higher...

I suspect what's going on is that the signal you're getting is not quite clean enough for a data transfer. You might be able to get a video signal, but I bet it'd be choppy, with frequent audio clipping. The data stream required is much less forgiving than your eyes and ears.

Get the installers back out to your house and tell them to bring another receiver. The installer who did mine had a couple receivers he used as test units, and even a small TV he carried on the roof! See if they can get a download out of your dish before looking at the receiver as the culprit.

Good luck!