the drop is probably from the a/c if it happened to coincide with the higher temperature

 

I got it in May, and ever since I bought it I've used the a/c quite a bit (I'm odd and can't stand driving around with the windows down, I find it annoying), and it didn't seem to cause too much of a drop. The one time I managed to get 18 I was driving around with both the front and rear a/c on high. The only real change has been the outside temperature.

 

not wierd at all, neither of my parents can stand driving around w/ the windows open either, i prefer it to the a/c, but then im alot younger too.

also keep in mind that the hotter it gets the harder the a/c has to work to provide the same level of cooling to you on the inside, when the a/c works harder it pulls more power from the engine making it work harder too.

i would very much like to know how you got 18 running with the a/c on, best i can get (even with highway driving) with the a/c on is about 17

 

It is the altitude, I know this sounds weird but many of my relatives that live in montana, colorado, and wyoming get worse milage in north dakota at our lower elevation.

 

I have an 04 Ram 1500 4X4, 5-speed, 4.7L. I have manually calculated my mileage on two trips traveling I-75 to Florida. Driving 70-75 where permitted, I averaged 16.9 on both trips, with synthetic oil on the second trip. The syn oil made no difference. Oh yeah, using the A/C both trips.

 

I got 18.8 actually, it was both city and highway, the difference between this and what I normally do, I took the old highway to Colorado Springs, where the speed limit is 65, instead of 75, so I was going 65-70 instead of 85. Then I drove around down there for a few hours. I would guess that I got at least 20 on the highway and then the city driving brought it down.

 

my normal cruising speed is 75 80 and i normally average 20 on the highway, idk how you manage that with the a/c on tho (yes i notice that i drive alot harder when the a/c is on which is why the difference is so large for me, normally it should be less)

 

The altitude probably makes some difference too, I would suspect I might not get 20 MPG so high up.

 

I usually get around 15mpg in my 4X2.

 

No it would be better at high altitude because less air means less fuel used.