GM fuel senders read between 0 and 90ohms chrysler and ford I think read something like 100-150(?)... if you have the wrong sender the gauge will be wrong. For the turn signals and dash lighting, have you checked all the dash bulbs? You mentioned you replaced some missing bulbs but it sounds like the turn signal bulbs are burnt out or the wiring to the dash has problems.

Welcome to here and good luck...

-Chris