[NY4x4]

I have driven nothing but Toyota 4x4 pickups since memorial day of 1993. This is my third one, 2003 Taycoma TRD, 5 spd, wine red with 30K. I love it but need a few questions answered -
1. My RPM's @ 65mph are a whopping 2500, (stock size tires)
2. Were different rear end ratio's avaliable with these TRD's??
3. If so, 2500rpm's @ 65 MPH 5th gear, would be what ratio?? 3.55's maybe??
4. Can I order taller gears from Toyota if mine are lower than stock??
5. Is the K&N filter system under my hood doing me any good or should I change it to stock??

Thanks!!