My mechanic road with us on a camping trip from Phonix up to Flagstaff, with lots of mountain steep grades. He felt the engine roar was a defective fan clutch. It happens when the truck is upshifting, it seems like it is not shifting. He put in a new fan (not a dealer fan) and it has been a year, and it has done the same thing the whole time. He thinks the new fan is deffective and that we should buy a toyota fan. Other folks think it is a switch in the tranny. It seems to have less power when roaring. Initially this seemed to be less of an issue at higher altitudes or perhaps it was the cooler air...... I'd also like some advice on upgrading the front brakes, they are undersized and I'm going to be towing a trailer. The truck has 155,000 miles.