id just like to know the reason that you loose 5th gear by running bigger tires without re gearing your t case

You don't actually lose 5th gear. The engine needs to run at a certain rpm to make power. They are geared to keep the engine in it's "powerband" with the stock 205/75R15 tires. If you add taller tires, you actually make the gear ratio higher due to the larger diameter. Now the motor does not reach it's optimum rpm range, and therefore can't maintan highway speeds in 5th gear. Lower gears, either t-case or axle, put the motor back in the right rpm range. Maybe I explained it, if not, someone else is welcome to correct me or add.

that answers my question exactly. 

I'm up to a 31" tire with stock gearing and I still use 5th everyday. It's really nice because moving along at highway speeds I'll only rev ~3000rpm. My spedometer reads a touch over 90km/h but I'm actually travelling 100km/h.

It's leverage. A wheel is really a lever. The longer the lever (bigger the tire), the more resistance the axle shaft (and therefore your engine) has. Then, there's the added rotational weight. Rotation weight is bad for the same reason.

make sure you have a full tune up, with perhaps best plugs and K&N type filter, so that the motor is on song, and that will help a little

just sit back and enjoy it!

Not a fan of K&N actually:
http://www.bobistheoilguy.com/airfilter/airtest3.htm

The K&N don't keep quite as much dust out, but they do flow a lot better.  I would rather use some of the new synthetic filters but nobody has made one for the Tracker yet.

I lost 5th gear, then I found it again.

Always the last place you look.....