so in all that.. all I saw was the starter spins the engine over slowly while Turing to crank? that sounds like the common battery cable issues these trucks get. sensor won't make it crank slowly, that's a lack of current to the starter motor. either weak. battery or corroded up cables, they seem to go bad from the inside out.
the dash doing funny stuff also sounds like battery voltage issues.
others will chime in, but I believe this is a case of replacing both the postive and negative battery ables and clean the grounding point the negative cable bolts to the block at.
then charge and load test the battery and go from there.