Hello,
The rpm's on my wifes Avalon drop like a rock when I put 'er in neut. Coasting @ 65 mph, with 600 rpm.
I tested several vehicles at work this way, practicing my P&G. Engine running.
Everything I drove from a 2006 Mack twin screw tractor to the 2002 Caravan. All had lowered rpm in neut while traveling at highway speed.
Caravan was worst. 900 at speed, 700 stopped.
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Mack was best. 550 at speed, 550 stopped.
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(All of our trucks are automatic. maintenance costs are lower than with clutches.)
BUT, all were way lower than your 1500 to 1700 at speed.
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I will get my hands on a newer Ford product and see what kind of results I get.
S.