since you are committed to this truck (unless brother will take back,haha), you might get the oil pressure switch, but before install, run some motor flush; then do oil change, and install new switch, and see if gauge results change..
if still low psi, then Stealthee is probably right.. an oil pump will help new pressure; but damage is probably already done..
here is 95 buick for 1200 (they listed caliber as well):
https://fortcollins.craigslist.org/c...301454178.html