I have a 2004 Xb 1.5l Automatic. I have owned for about a year and lately I have had tons of trouble with it not shifting into 4th/Overdrive. It just happens randomly. This really sucks for me since It is all highway to travel to work and I am pinned at 3300 rpm trying to at least do the speed limit so others don't run me over. I know this is hurting my car and tearing it up. What is the problem?

Also my car has started to sound like a moped like there is a leak somewhere in the muffler under the motor. Makes me feel like someone is pulling me from behind and I can't accelerate. This an easy fix?