I fixed — somewhat — Kevin’s truck this weekend. It turns out the fuel pump did not need to be replaced; the fuel tank was almost empty. Once I put five gallons of gas in it, it started up — but still ran like crap.
I looked into things I could do to troubleshoot. One of those things was to unplug the throttle position sensor, as the truck’s symptoms (backfiring, hesitating on quick acceleration, lack of power, failing to idle, poor shifting) were consistent with a bad TPS.
It drove better after unplugging, so I spent $48 on a new throttle position sensor at AutoZone and replaced it. The truck runs and drives amazingly better now. It still wants to not idle well immediately after startup, but then the idle smooths out. The backfiring is gone, as is hesitating on acceleration and poor shifting. Power is still not where it should be, but there are several other things that could be causing that.
At this point, the truck is driveable, which means it’s registerable.