2002 Sonoma Oil Pressure Variation

[DVL]

I own a 2002 GMC Sonoma 4.3L, with 77K miles. It's been dealer serviced every 3K miles since new. Within the past 10K miles or so, the oil pressure has reduced from 30+ psi at warm idle and 40-50+ psi at engine speeds > 1000 RPM (warm), to 20-25 psi at warm idle and just under 40 psi at engine speeds > 1000 RPM (warm). The oil pressure gauge fluctuates about 5 psi when engine speed returns to idle then stabilizes at 20 to 25 psi. Under increased load (driving up hill, for example), I've also witnessed about a 5 psi drop in oil pressure a few times recently.

 

Is this normal operation? Is this an indication of an upcoming failure (bearings, faulty oil pump or oil pump by-pass, etc)? My dealer states these symtoms are normal for 4.3L's and recommends possibly using an oil stabilizer such as Lucas or Slick 50.

 

Thanks for your help.