"First are you even sure you have enough truck for a 43' footer???" hmmm....appropriate question. My 37 footer is 19K loaded for travel....which led me to upgrade my truck...I found my 5.9 had plenty of pulling power, but no where near adequate stopping power.
And when you say "you can ask the salesman" for information...most of us have learned that is usually not a good idea, unless you want the moon and three acres of cheese along with your answer.
I see you joined this forum 3 days ago....I'd say keep reading and asking questions before you purchase anything.
Regards
Gemstone
