Specifically, trying to gain lean muscle mass?

Tell me what I'm doing wrong here, I'm 5'10" & 160 lbs...


Free Weights:

Bench: 50 lb dbells - 3 sets of 10 to 12 reps
Flies: 45 lb dbells - 3 sets of 10 to 12 reps
Curls: 30 lb dbells - 3 sets of 10 of standard, twist, and hammer each
Shoulder Press: 25 lb dbells - 3 sets of 10
Shoulder Front & Lateral Raises: 20 lb dbells - 3 sets of 10 each
Tri's: 20 lb dbells - 3 sets of 10 to 12 (lying on back one arm at a time)

Sit-ups: Multiple sets of 25 each, rotating w/feet on floor and feet raised (knees closer to chest)
Push-ups: Sets of 10 whenever I remember to squeeze them in away from the gym

Legs: Nothing. Cardio more than takes care of this? Quads and calves have very good definition.


Cardio:

1 hour on the stairclimber 4 to 5 times per week and I don't go easy. I usually do the pre-set "Rolling Hills" program at a level 10 setting (20 is the max) and I don't hold onto the side railings, my arms swing freely. At the peak points on the hill, I'm literally running on the **** thing. I do this in three, 20 minute intervals, resting for a minute in between to stretch and to drink water. This definitely gets the heart rate going and I sweat a good bit.

Food:

Tons of pasta, chicken, salads, sandwiches, raw broccoli, Grape Nuts, Cheerios, Raisin Bran, Power Bars, hummus, low-fat cheese, low-fat Trader Joe's frozen foods, peanut butter, almonds, cashews, everything whole grain as much as possible.


Just can't seem to get bigger, thicker muscles. I have more of a runner's body, which I don't really like. Decent muscle definition but severely lack density. Odd thing is, outside of the real meatheads at the gym, I don't lift weights that are significantly much less than others, but I'm a good bit smaller than most. I've been working out consistently for a good 10 years, not always the same routine mind you, but a combo of the above.