Just read this whole thread and must say that you REALLY did a ton of work!

The white smoke (although just a little) kinda tells me that the valve stem seals might be leaking BUT you installed a new head so that suggestion doesn't make sense! hhmmm...

Anyway, the thing that caught my eye about your fuel gauge and pump.... the ground wire for the tank and pump (they are one common wire), runs through a pair of connectors right around where the bed meets the cab.

I watched a video from scannerdanner about a ranger with low fuel pressure and the ground wire was all but broken!

Water had gotten into the wire and corroded the copper to the point where only one or two strands were still connected and couldn't carry the full current for the pump and the gauge, and when the parking lights were turned on, the fuel pump would not run and the fuel pressure would drop. This was due to the parking/brake light current drawing additional current through the same wire.

Not saying that this may be your problem, but it might be worth checking out the wire bundles under the bed/cab.

I had a problem with my truck (99 Ranger XLT 4 door), where the hot wire to the pump was rubbing on the bed because it was too long, and actually rubbed through the insulation and shorted out, blowing the fuel pump fuse! INSTANT engine turn off!!

Happened at work so wasn't real convenient, but when do these things happen??