Slow acceleration sometimes on 1997 Chevrolet S10

Lately I have noticed my truck bogging down especially when it has sat all night or all day while I am at work. Although, it does this only sometimes which is the puzzling part. It just won't go when it acts up, then I can either shift into 2nd or just give it a minute, and it picks up. However, the other day it did this through 3rd gear. My Service Engine light came on the other day so I took it to the shop where he pulled a MAF Sensor malfunction along with lean on banks 1 and 2. What do you think?
I have replaced the 02 sensors, distributor cap and rotor, plugs, wires, fuel filter all at 100k. I only run royal purple oil, along with k&n oil and air filters. Replaced the fuel pump @ 30K miles. I just want my truck to run right, I'm not ready to give her up yet, although my wife would like to see it go.

Asked by for the 1997 Chevrolet S10
Not being able to drive the truck first hand it is difficult to guess without having performed diagnostic tests. I don't work on Chevys and the only reason I am responding is a friend of mine had a very similar problem,same conditions, he had previously blown a head gasket and the valve springs had failed. It was bizarre but the garage that checked it out said they had seen it before on the S10. Totally a guess. Have the truck properly checked out using a scan tool look at live information as the truck is drive, mount a fuel pressure gauge to the windscreen and drive the truck to pin point the problem.