Ok so im driving at 45 with the cruse control on and decide to do 40 instead and when i got to 40 the rpm increased. I thought I was seeing things so when I got to the next light I put it in test mode to see a digital rpm meter and I was correct. At 40 the tach read 1250 and at 45 it was 1200. This was on a smooth stright flat road. I had to go up to 47 to get back up to 1250 rpm. Seems kind of strange to me. I guess its cheaper to go faster in some cases.

 

Probably because it was too slow for OD. It shifted down to 3rd.

 

At 40 mph my tach shows 900 rpms. Because I am in 5th.

The only way to get off by going slow in a vehicle is if you were driving a stick. An automatic inherently wastes gas, and lots of it. I figured that out driving a rental F150 with the triton 5.4l... that thing would just sit there happily running at 40 mph at 1250-1300 rpms... when in my mind that thing could have been at 900 - 1000 rpms.

 

Around 40 MPH is the shift point for overdrive. If you are going that speed with any load on the engine at all, it will downshift.

 

The others hit it one the head. The tranny shifts in/out of OD right at 40-45 mph. The truck is not going to maintain OD at 40mph.

 

You wont sell me that 200 rpms is going to make much difference in gas mileage. You have to look at engine load, throttle position, etc, etc. There is more to MPG than just RPM.

 

The difference in RPM's is either because it downshifted to 3rd, or it was still in 4th but the torque converter unlocked.

 

Thanks. at least its not another I got a problem with my truck.

 

absolutely, good post hllon4whls.