Ive been driving my wifes crv for about 3 months now and at first it would get about 300 miles to the tank. However I noticed that when driving down the highway it seemed to stay at a high rpm ( about 3100-3200 @70mph ) then i could feel another shift and it would drop down to about 2800rpm. That was back in october and i only noticed it on the really cold days, now that it has gotten colder it will not shift into that next gear and drop the rpms. My mpg is suffering as a result and now it gets about 260 max to the tank. Ive counted the shifts now and it gets to 4th gear and thats it, is my trans slipping or does it have a 5th gear that its not shifting to? Local guy thinks it may be a solenoid, car and trans has 243K on it with a new swap with 5k on it since the swap.

 

A 99 is a 4 speed automatic.

I think you are seeing torque converter lockup when the rpms drop. I think those will throw a code and light up the dash if lockup is not functioning as expected.

Not unusual for MPGs to drop in the cold weather.