Check the voltage between the battery and the fuse box ( the lead that goes to the front of the box under the little cover). Touch the negative side of the battery and the fuse box lead. The voltage should be the same over that as well as the battery. If its anything less you need a new cable. Do the same for the starter
I know a lot of ppl that have had the cable die. Make sure that all of the connections are clean using electric cleaner.
I know you have probably already have done this, but try and wiggle the wires around this time because it can have a short in the line and not know.
Hope this helps
RE 3.5 SF w/ adj arms, S-10 4" leafs, Front hitch, rear DIY bumper, 31" BFG ATs, D-Window w/ 4.5 BS