My 4Runner recently had the MAF sensor and fuel pump replaced, but still hasn't been running completely right. It doesn't stall anymore, but it accelerates even slower than it's supposed to -- I basically have to use full throttle just to get up to speed. I did a little testing today between a couple of nearby freeway exits, and my 0-60 time was something like 30+ seconds and after I continued to floor it up to about 70 it eventually threw a code 25 (mix continuously lean).

I've been reading some other threads about code 25 problems, but it seems like most of those folks had problems with sensors or air leaks (too much O2), whereas my problem really seems like it's running lean due to too little fuel. Any ideas of what I should do first to troubleshoot it?

 

When was the fuel filter last changed?
You can check the flow rate by connecting a clear tube to the FPR, and thence into a container to catch the fuel, and seeing how much fuel you get in 30 seconds or so. I believe the usual amount is about 500 mL in 30 seconds. Much less, if you have a new filter installed, it's time to start cleaning fuel lines from the tank to the fuel rail.
If it's OK, you might consider getting the injectors cleaned/reconditioned by a professional shop. A good shop usually takes about a week, including shipping both ways, depending on distance.

Did you check the pressure once you replaced the fuel pump? That's important too, after all.

Good fortune!
Pat☺