bad batteries or batteries with poor connections can cause all sorts of weird issues. and bad starters can cause bad batteries or the extra current can heat the wires or connections and they get high resistance. basic rule of trouble shooting on a complicated system like a car, start at the power source and make sure everything is good there and dont worry about multiple issues, may be all related to that but if it is you waste time trouble shooting things that arent the problem. if they are two problems you would have had to work on both anyway.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock