I have a 97 K1500 w/5.7L and 251K miles. Just noticed the other day that the oil pressure was unusally low. It usually runs about 45-50 psi (per gage on dash) at highway cruising speeds, however it now stays around the 30 psi range. I would think that if the oil pump was getting weak it would be more gradual. Just changed the oil and the presure hasn't improved (10W30). The pressure also fluctuates quickly sometimes at constant rpm. Are the oil pressure switches prone to aging reporting lower pressure than normal ? Where is the switch located?