I still would think u-joint operating angle, but don't know for sure.
Gas tank for the lean? What else is over there that we can blame it on... Master cylinder, interior stuff.
I know solid axle Yotas lean because from the factory, one front spring mount is put up higher than the other to clear the diff. Stock springs are made to compensate for this, but most aftermarket ones are not.
Have never taken an eye at my front axle closely enough, but my MJ leans a bit too. I just blame it on the tank.