deanofay

i went on a 250 mile trip this weekend towing a 6 by 10 closed trailer. i live in florida where it is as flat as a pancake and my truck(2003 4.6l v8) was unable to pull the trailer in overdrive so i had to keep overdrive off. My first question is that the truck with overdrive off was running at 3000 rpms?? i believe that to be third gear why doesn't it stay in 4th?. Also with a cold air intake, exhaust, and custom tune shouldn't my truck be able to pull the trailer in overdrive?