I know this doesn't help, but it depends. First I don't know what motor you have. Some motors like the Tenshock are absolute power hogs. It also largely depends on how your driving. If you stopping and accelerating a lot, that's going to use power more than simple cruising around on a flat track.

Just some rough math. First I don't know what 4700kv motor you have, but it probably has a max power rating of anywhere from 300w to 800w.

Let's just take something in the middle, 500w. Roughly, w = a * v (I'm ignoring power factor or efficiency here). Over the course of a discharge your battery would have an average of 7.6v, so w/v = a or 500w/7.6v = 65a

Your battery is 6.5a hours, so 6.5a/65a = .1 hours or 6 minutes.

Now that's assuming things like your motor using it's max power the whole 6 minutes which would be impossible.

But I also don't think you would get 30-40 minutes out of it. Especially since 4wd SC trucks are typically heavy and have lots of drivetrain resistance.

Plus depending on the C rating of the battery, you might be hitting LVC because of high voltage sag under a high load from motor in your truck.