I heard a rumor that if you put your tranny in tow/haul mode while cruising at 75 it will make the motor go into v4 mode resulting in better fuel economy

 

try it and let me know!

 

On the highway it doesn't make a difference for me, I think it is probably the wind resistance. However, cruising around town it definitely makes a difference. The ride is a little harsher (shifting) but it does help it stay in V4 longer and not just when coasting. There is an art to it, you have to be light on the pedal but it works.

 

I'd be surprised if this actually helps because every vehicle I've ever owned with a tow/haul switch disables the overdrive & lockup in the torque converter. Resulting in higher rpm's / less economy/ more drivetrain wear. Also, I did notice a shift pattern change when in tow mode which appears optimized to keep the rpm's & torque curve up.

 

With the Tahoe and alot of newer vehicles the tranny will go into lock up and overdrive in tow mode, it just does it at a higher RPM. And using tow mode increases the line pressure resulting in a harsher, quicker shift which is actually better for a tranny. A longer smooth shift is actually harder on the transmission.

 

I've tried it in town at 35-45 mph and it definitely improves mpg for me but you have to go back to normal when on level and downhill to get back in to OD and lockup. Saw no difference at hiway speeds as it stays in OD & lockup. Biggest change came when I went to Mobil 1. About plus 0.5 mpg calculated over several tanks.