freeway driving, 3rd gear uphill?

[palemelanesian]

The air filter will help ONLY if the old one is really really dirty.

San Francisco? I can believe you might need 3rd sometimes. It would still be better to gain some speed first and hold 4th if you can.

[Mayhim]

My air filter on the truck would tell me when it needed changed. I can drive from Omaha to KC on cruise control without it ever downshifting on any hills. One hill, though, would require downshifting when the air filter was getting full. Changed the filter and no more downshifting.