New Owner/Change all fluid in Rear end, trans and engine on TV?

I was told as a safety factor and for longevity before I tow my 2720SL to flush/drain my transmission, rear-end and engine and replace the old regular fluids with the new synthetic fluids for longevity and reduced wear. Is this an accurate suggestion? It was stated since I was close to maxing out my vehicle's towing capability it was even more important.

Ron Smith

149,000 (highway miles)