I wouldn't worry too much about sticking to 2500. 3 to 4,000 going upgrade won't hurt and is better than "lugging" the motor at low RPMs. Actually your auto trans will downshift as needed going up as that what it's for but doing it manually is a little better if your comfortable doing it. Down shift a little ahead of time not going to such a low gear that the engine screams. You can feel the motor starting to pull down as it needs a lower gear. Going down, the auto won't do the job on it's own. Slow down before the down grade and keep slowing and downshifting 1 gear at a time until you can coast along without much braking. On a real steep one, you may need to brake a little but I seldom need the brakes on main highways. Above all, slow down.