ran the car on fumes, having stalling problems

[MrSpArkle]

Hi guys, I need some help.

A few days ago I absent mindedly got on the highway with less than a quarter of a tank of gas, I figured I'd be cutting it close, but I'd be ok. After i got off the highway i noticed my car was sputtering a bit, so I filled up on gas, but it still sputtered, the idle fluctuated, and low end acceleration was horrible, and top was so-so. The problem has persisted, despite a fuel filter change and a bottle of techron(which helped a little bit, but it may have been placebo). The pattern is as follows:

Car runs semi ****ty in morning (rpms dropping below 500)
Car improves during middle of day (still not as powerful)
Car degrades at night (car starts to stall)

It's not a strict pattern but it's as close as i can describe the car's behaviour from day to day. My best guess is that I either ****ed up my fuel pump, or clogged up something because of my low gas level. I have tried the following:

Fuel Filter Change
Techron
Ensured all spark plugs are working
Checked vacuum lines
Listened for weak injector (none sounded any weaker than usual)

And have performed the following service within the last 2 months:

Air filter cleaning
Plugs+wires
Oil change
Timing chain guide removal

I'm about to go and get some fuel injector service done, today I shoved another bottle of techron(have yet to run the car hard), after that it's off to the mechanic, unless you guys can come to my rescue.

91 240sx fastback
k&n filter, custom headers+exhaust, and alot of dreams.