Poor Engine Performance and poor fuel economy

What is your question?

Actually I have an E450 SuperDuty Cutaway Chassis for a C Class motorhome. Have complained to Ford about poor engine performance and fuel economy. Ford told me I was still breaking in the vehicle. Ford fixed the air intake after I notified them of the service bulletin, but it still lacks power going up hills and in high altitude 1,000' and above. Plus on flat land it only gets 6 mpg! Transmission "clanks" when shifting into and out of park. Ford told me it was because of my long drive shaft. Oh please, it's a 24' chassis! I am a former Cadillac Parts Manager and a woman, YIKES! Please advise.