My Envoy is approaching 170000 miles and has developed an engine noise like a rod bearing knocking. I have my OTC mechanical oil pressure gauge installed. At a cold startup, I see 80 pounds of pressure on the gauge and have no engine noise at idle. Driving down the road, the oil pressure gets close to 95 lbs at approximately 2000 rpm then drops back to 80lbs when the transmission shifts into second gear. After everything warms up to operating temperature, cruising at 65 mph, I'm seeing 70lbs on the pressure gauge. I hear no noise driving down the road. When I come to a stop with the engine at idle in gear i have 26 to 28 lbs of oil pressure, and the engine is quiet. When you take off again at about 2000 rpm, just about the time the transmission changes gears, it sounds like a rod knocking . In park after the engine is at operating temperature, if I bring the rpm up to 2000 rpm, it sounds like it is knocking. When the engine was cold, I pulled the spark plugs and brought each individual piston up to top dead center, starting on the down stroke, I took a wooden dowel and tried to push each piston down to check for a bad rod bearing and didn't find any. I again brought the engine up to operating temperature and using my Tech2 scanner, I did a cylinder balance test at 2000 rpm. Each cylinder dropped the same rpm but the knocking noise never changed. I'm at my wits end here. I have access to another low mileage engine but I'm unable to perform the swap myself, so before I spend the money to have it swapped, I'm looking for suggestions.