Your getting excellent advise.
If you have a remote starter switch (don't cost much at your LAPS), you can connect it directly to your starter and bat and engage it while on your truck. This may help you isolate the issue.
I may have missed something, but sounds like there's a big drain on your battery. (short somewhere??)

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter