I just bought a used 2000 xe 4cyclinder. I've had it for about a month or so. I found out so far that the gas mileage could use a little improvement. Maybe a lot . My boyfriend wants to change the stock filter to K&N. But from reading the thread, I would prefer one that can be cleaned with just air. Plus I live in san diego beach area, so there is a lot of dirt particles in the air. I"m switching the oil to all synthetic. What type of oil should I use? It does get pretty warm around here most of the year. The shifting seems a little rough too. What would you guys suggest? Anything else I should do? There is a little over 115K on it so far. I'm also getting all new stock tires from bfg. I read earlier it is best to have them at 28 psi, but then read later to have it close to tire recommendation for best ride and mileage. Which is it? Also, it seems to take a while to get up a hill. Kind of sluggish. Is this normal for such a big vehicle running on 4 cyclinders?