I can understand your concerns. An inch or two of sludge in the oil pan is a boatload never mind 5 inches. Normally sludge that is present in the pan would indicate that the valve train is pretty much loaded with sludge as well. With regards to the oil pressure light this is dictated by the oil sending unit. If a relatively small amount of contamination affixes to this sensor then the motor ECU or computer can get a bad reading and trigger the light. I am in agreement with your mechanic that running a quick solvent flush could be disastrous, chunking off large pieces of hardened sludge. The best way to proceed would be with a slow methodical cleaner, which is Auto-Rx. However, based on simple oil changes at 1000 miles do not do much cleaning, I am concerned that you may have an issue with coolant getting into the oiling system, creating more sludging in short order. Also you will want to check the performance of the PCV valve in this unit. If the valve is stuck or the hosing is plugged up, then all of the blow by gasses are trapped inside the oiling system that is also a prime catalyst for sludging.
My guess is that your unit has the 5.7 liter V-8, or 350 cubic inch motor. These motors are not normally sludge prone , unless there exists one of the situations previously mentioned. On the other side of the coin these are very durable motors.
I would suggest that you proceed as follows. To a fresh fill of conventional oil, with a new filter in place, add the entire contents of 1 full bottle of Auto-Rx. The plan is to operate this oil change for 2500 miles with one exception. That would be to change out the oil filter only at the 1000 to 1250 mile mark. Then proceed on to 2500 miles total. At that point change out the oil and filter and run another oil change interval for 3000 miles. Again with one exception, change out the filter at the 1500 mile mark or half way. You will need to perform this procedure twice. It may or may not be necessary to change out the filters midstream on the second go around.
The beauty of ARX is that it works first on areas that have the most oil flow and heat, in other words, the working parts. It is key in your situation that initially cosmetic areas of the motors internal dont clean up right away. The key is to get the key working parts cleaned up first.
The third bottle can be used as a maintenance dose. That is adding 3 fluid ounces to each oil change after completing the steps outline above, to each oil change to continue cleaning or at least maintaining the gains achieved from the two cleaning applications.
I hope this information is helpful. If you have any further questions, please reply.
