I'm used to the accelerator pedal being able to go to the floor on my 01 Malibu. But my Maxima doesn't, it goes about halfway and won't go down further. Is this okay?

Even bigger of an issue, is that because of this, I have difficulty getting it to accelerate above 40mph. I'll have the pedal depressed as far as it will go (halfway) and it tops at 40, the RPM kicks in like normal (gets to around 7k(?)) but the car sluggishly increases speed (takes a bit to get to 41mph, 42, etc...).

Any possible diagnosis?

 

Something is probably wrong with the throttle cables. it might be binding somewhere.
Open the hood and make sure the throttle plate can open all the way. It would be good to have a friend push on the gas pedal while you look under the hood.

I installed the clamp that attaches the rubber boot incorrectly. It interfered with the throttle motion. I learned that when I hit the gas hard on the freeway. Throttle stuck open while I was going uphill in the middle lane. Not fun.