Mwc

I have a 2018 2500 with 4-10 gears and a 8 speed transmission. I live in north east Texas with flat ground. My RV weights roughly 6500 lbs and I cant run 70 with out thinking I am going to blow it up. This truck dont even like my 5000lb welding trailer. It now has 15500 miles on it and I have tried every kinda gas they make . It's been in the shop 3 or 4 time to see if something is wrong with it and they cant find anything. Not happy at all with this pig