Engine Sludge (auto-rx)

I have a 2000 Dodge Durango SLT 4WD with 48k on it. It has a 4.7L in it. I recenty noticed that there was sludge under my gas cap, which implies there is also sludge in my engine. I discovered this engine treatment called 'Auto-rx' that is supposed to liquify the sludge and deposit it in the oil filter. So, I started the treatment and have just finished the wash phase. The engine oil is very dirty after driving just 1500 miles, and I have noticed that my engine performance has improved. I have also noticed a slight increase in my highway mpg (increased from 17 to 18 per the digital readout in the overhead console). The treatment seems to be working well, but it's hard to say for sure without actually looking inside the engine. Has anyone else used this stuff and know whether or not it will save a durango engine? The website is:

www.auto-rx.com

Thanks,
Dave K.