Tranny swap

Is it possible to connect a 6spd tranny to the 4 cyl. I have a 05 Tacoma. 4x4. Ext cab.

 

its possible.... but the 5 spd manual on the 4x4 is so much better of a trans compared to the 6spd manual of the v6's

 

Just looking to get better gas mileage on the highway

 

The 6 speed most likely won't get you better mpg. The gear ratio is much lower, and with the little power the 4 cyl has you'll most likely be down shifting often to maintain highway speeds. But like it was also said, the 5 speed is waaaaaaay more reliable. Best advice, just drive like an old lady, keep the revs down, stick with the oem tires, keep extra weight out of the truck.