i'm sorry i wasn't very clear.
what i ment was when my truck hits the speed limiter it completly cuts out like you turned off the ignition then once u've slowed down the engine kicks back in.
Im pretty sure it does that buy cutting power to the coil or fuel pump.

you said it acts like its completly shutting off and coming back on causing bucking.
so i just thought that maybe power was getting interupted to the coil or the fuel pump

but unfortunatly that doesn't explain the lean reading ur getting off of ur O2 sensor or why ur getting a -0.5V when the lower limit should be 0.0V
That sounds like a crossed wire, but u said the reman engine ran great till this last spring so i dont see how a wire could get crossed.

that leads me back to the fuel diverter valve i think that is your best bet right now.
I had a 1987 F-150 302 4x4 XLT Lariet that i worked on that had a very similar problem, it would run great for about 30 sec to a minute then it would spit, backfire, cough, buck the whole 9 yards turns out i had 2 porblems
1. the intank fuel pump was bad
2. the fuel diverter was actually sending the little fuel it was pumping from the rear to the front tank.
Now since you just replaced the pump i think whats happening is the FDV is the check ball is messed up and not allowing the fuel to go the the right place.

Now i know what ur thinkin in that if its cutting off fuel why does it look rich and the O2 says lean? well im not sure about that but mine had enough black smoke come out of it to make a cloud behind the truck and it WAS starving for fuel.

what we eventually did is use a cheap fuel filter and use that to make the connection becase it has the ford fuel line ends on it

sorryfor the long winded post :P