Mines a manual so I can't say how it will have an effect on your auto. I do idle at about 10mph in first now, with 3.73. I do need to regear. I didn't originally because I had stock sized 14" tires before and hatred 3k at rpm 70mph. Now I don't go into 5th until 60+.
As for the ride, it's much smoother and feels nicer, you don't feel every single bump or crack in the road like before.
My suspension lift only took the front up an inch higher that the rear, so if I were you I would measure front and rear hight, put a jack under the front and lift till it's even and measure again, but like I said, my springs and shocks were shot. Then again my truck is almost at 250k on the clock.