with tall tires, you should be fine running 55 on the highway. I ran up to 65 with mine with the stock 4.11 gears and stock tranny.
The next step is to put in an OD tranny - you will not find a better ratio (numerically lower ratio) for that housing unless you find the very rare 3.90 which is hardly worth the effort if you already have a 4.11.
I have an A833 tranny which gives me a 0.73 OD for 4th gear - would make 70 mph a dream at about 2500 rpm with your setup.
